take off the cap & check that the rotor is retracted all the way (it should be from the springs unless the slots/pins are gummed up). loosen the holddown clamp & turn the dist housing slightly a bit till the magnet is dead even with the closest reluctor tooth. tighten the clamp.
Make a magic marker mark on the side of the dist housing straight down vertical/plumb from the rotor tip clocking. replace the cap & make another magic marker mark on the dist housing side inline with the "bulge" of the particular cap terminal where the rotor is located at which will be pretty close to your first mark. You want the rotor at rest to be pretty much clocked right at the cap terminal bulge center & the can will shift RP CCW on a SB so ideally you want the rotor to be a bit CW from dead centered. edge to edge in a vertical plumb CL is good. You do have some leeway there cuz the cap terminal is .214" wide and the rotor terminal is .244" and the can shifts the rotor .023" around its travel arc for every degree stamped on the can. also check the rotor tip to cap terminal clearance, ideal is to reduce it to .015" by drilling out the rivet & makeing your own blade. On OE dists, the reluctor gap opens up as the can adds advance so if your dist does not then that is a bennie. Are you sure yours is staying at the same .008"?

Yes I'm positive, before installing this firecore distributor I removed the cap and
Checked all 8 reluctor blades to pick up coil post clearneces with a brass feeler gauge, all of them were at .008.
I then hooked up my brand new mity vac hand pump to the vacuum advance and deployed the vacuum advance untill the arm was fully pulled out and I held it there with the mity vac while I went around each tooth on the reluctor and again they were all at .008.
The rotor that came with this firecore distributor already has a longer blade then the factory rotor blade.
I was thinking about buying a cheap distributor cap and drilling a hole
In it by the number 1 plug tower and then hooking my timing light up to it and watching it at 2500 with the vacuum advance plugged in and then I can get an idea of how far off the phasing is.
Then I suppose I could ether buy the reluctor that Rick ehnberg sells that has multiple key ways cut into it for rotor phasing, or I can buy another cap and modify a new slot on the base of it to put it on the distributor.
Or I could send it back to firecore and make it their problem to fix it cause it's still under its warranty.

Another option is I can pull the distributor and change the mechanical advance to increase the timing a little more and then I can back off the vacuum advance a few degrees and see if that's enough to correct the issue.

You might call Firecore ask them about returning it. Yes you can drill a 1/2" hole in the top cap flat 2/3 of the way from the center cap terminal over to the #1 cap terminal to shine your light into to check RP. You can redrill your reluctor yourself: drill a bit inward from the ID then use a mini round rat tail file to open it up/break thru to the ID. carefull measureing & if you are too far off there is plenty of area to drill several of em. First try the BB OE roll pin hole. here is one in progress. EDIT I gotta figure out how to work this camera.

The issue appears to be solved, I increased the initial timing from 16 to 18 which made my total go from 32 to 34, I then dialed back the vacuum advance to add 12 degrees of timing to the 18 at idle for a total of 30 at idle.
I had to turn the screw inside he vaccum canister about 4-5 turns outward to get it to drop the timing 2 degrees.
I think the vacuum can was wide open on this distributor and it was just advancing it too far and throwing the phase off.
I haven't driven it a whole lot since dialing back the vacuum advance but the little drive I did go on tonight I took it up to 3000 rpm in 2nd gear and held it there for awhile waiting
To feel the miss fire and never did.
So it appears to be solved, but I will drive it more in the next couple of days and report back if I find any Miss fires through out the rpm range.

That is real good to hear (& didn't take alot of digging in which wouldn't have been fun).

So now I am left pondering about
"Drilling out the rivet and making your own rotor contact"

On a Magnum style V8
with slotted flywheel and crank position sensor triggering,
if you wanted to custom retard cylinder number 7 a bit,
could you custom make a rotor with wider tip
And grind away part of number 7 cylinders distributor cap post?

to do that you would need to change WHEN it gets triggered. A larger gap might only delay the flame arrival by half a nano second, not near enough for what you are wanting to do & if the available voltage is greater than the required voltage to jump a certain gap then all is good there as it will fire but a minimal gap is needed at WOT as cyl psi is higher & coil rise time available is less and sparks blacken the brass contacts & any spark outside of the combustion chamber is wasted energy & kudos to you on doing this, Smokey Yunicks take was to individually dial in each cyls timing/CR for max power, treating each cyl as an individual powerplant. Tho for our apps octane would be the limiter on the DCR.

So as promised I'm back to give an update.
I drove the truck around a little more today and was able to test it out better with more open road and a longer drive.
I can still feel a very slight miss fire type vibration that comes on around the same time as before 2500-2600 rpm, but it is about 80 percent better for sure.
So my question is does mechanical advance affect rotor phasing? Or is it only vacuum advance that affects it?
And my next question, is there anything else I can do before modifying a distributor cap that lines up better with the rotor blade?
I was told I could file down the edge of the rotor a little bit the side where it spins under the contacts to help give the spark a little smoother transistion to the cap terminals.
Thinking about trying that.
Im also considering calling firecore and explaining the issue and seeing if they are willing to fix it.

Only vac advance affects Rotor Phasing, mech adv or initial timing does not. I would highly suggest modding the reluctor as opposed to altering the cap which will cause problems as that (2 side clips etc) is a flimsy system). I would just drill another roll pin hole in the reluctor & you're all set on RP then if that ain't it then we can continue on. How far is the RP off now?

I'm not sure how far off it is, I haven't had a chance to buy a cheaper cap and drill a hole in it to watch it, but I know that's what this issue is, because when I un-plug the vacuum advance it's completely gone, and like I said turning the vacuum advance down some made it a lot better but with the vacuum advance turned down a little and hooked up I can still feel it going on but it's not as severe.
I wonder if the guy at firecore has a distributor machine? I'm thinking about calling them and explaining what's going and what rpm and what the vacuum is so that maybe they could mimics the situation on a distributor machine and watch the rotor and then know exactly where it needs to be.
I guess I could do the same thing with a different reluctor, I just don't want to void my year long warrajtynon the distributor by modifying it or parts on it in case I run into other issues with it later on.

Oh OK I see what you are sayin, you don't want to void the warranty. Yes call em & go from there. post what they have to say. I would drill another hole in a cap as that is likely what they might ask, is how far off is it? EDIT You wouldn't want to send it in just to find out what you can find out yourself (how far RP is off). One other thing I would do now is bump up the timing/RPM to where it was acting up before (with the can capped) to see if it strickly a RP issue & not timing. You would need a dialback.

I have a digital dial back light with rpm read out.
I have capped the vacuum advance brought the rpm up to 2500 while
In nuetral and didn't hear it Miss firing.
And I've also capped the vacuum advance and drive it and don't feel it anymore.
I'm going to call them this afternoon and see what they say, is gonna ask for permission to fix it myself without housing the warranty if they say that's ok I'll modify my own reluctor is they say no I'll ask them to modify the reluctor

if it missed at 2500 steady RPM with the can hooked up then you might run it up to 2500 with the can capped then bump up the timing however much the can added (a 13 dist plate adds 26 degrees) & see how it acts & they will likely be asking for a timing number when you call.

Oh I see what your saying, advance the distributor to where it's at the same amount of timing as it is with the vacuum advance hooked up at 2500 rpm to see if it's still there.
That makes sense, my mechanical advance is set at 16 degrees, initial is at 18 degrees which makes the total at 34 degrees.
Vaccum advance is adding around 12-14 degrees at 2500 rpm, so that would be around 46-48 degrees of timing.
So I can increase the initial timing to 30 degrees on the distributor and leave the vaccum advance capped off and that would put my total timing around 46 degrees.
Is that going to be safe to do while holding the throttle steady at 2500? I don't see why it wouldn't be since the vaccum advance puts it around the mark anyway.
I will double check what the vacuum advance is adding at 2500 and then increase the distributor timing only to mimicking the same timing events to rule out any other issues other then rotor phasing.

Now since vacuum advance is the only thing that affects rotor phasing, I can also pull the distributor from the engine, throw on a different cap with a hole drilled by the number one cap terminal, apply my mity vac to the vacuum advance and then turn the distributor by hand to watch how far off it is from the cap terminal too correct?
This seems easier then trying to be over the top of my engine while it's revved up to 2500 trying to look down a little hole with the timing light.

You'd be surprised how inaccurate many of these are, esp the cheaper units, they'll have you chasing a "ghost" when it's the gun all along....

IMHO, buy yourself a basic/standard quality timing gun, or at least one to confirm the results/settings with your dial back

I've compared my light to two other lights and it's always the same, and I know my balancer is correct, I've verified it with a piston stop.
My light wasn't a cheap piece of crap ether.
I have the digital dial back light and then a regular dial back light, they are within a degree of each other, the older light will read a degree lower then the new digital light.
Another question for rapidrobert, what size drill bit will I need to add new slot to the reluctor? And will my idea work? Can I pull the distributor and apply the mity vac to it and then spin the distributor by hand to see how far off the rotor is from the cap terminals?
,

for a static (non rotating) test you could line up the magnet to a tooth. install cap. make a mark on dist metal side below the CL of the dist cap bulge (just below the bottom rim of the cap). take off the cap & see how far the rotor clocking from that mark then pump it up & see how far the rotor is from the cap bulge CL. make sure the springs are retracted & this test is "close" cuz the ign fires when the tooth is "just" moveing away from the magnet & it is hard to dead on visualize that timing (make sure the tooth stays dead even with the magnet, putting the lower tang in a vise works good). (best way) you check it running with your cap with the 1/2 hole in it, at idle with the can vac nipple capped then with it still idling pump up the can with the mityvac & see how far it moves as you have the light on it, (dont forget to have the DB back to zero), no need to do it at 2500. If it wont run with that much timing then rotate the dist back. Since RP ain't RPM/initial timing/mechanical timing dependent you don't need to have it at 2500 to check. On the 2500 RPM timing check if it was misfiring with the can hooked up at a total of say 46 degrees then run it up to 2500 then unplug the can/cap the nipple & turn the dist till you have 46 deg & see what develops. IIRC you turned the can innards with the 3/32 allen wrench & it got better but if the vac amt at the can is above what it takes to max it out at then the RP change is gonna be the same, it just that CCW with the allen wrench makes it take more in hg to max out at so check on that & you have a huge advantage haveing a Mityvac to play with. I don't remember offhand what size drill bit it takes but at least on an OE reluctor you can look down at the unused roll pin hole to fit a drill bit to it to get the size needed.

Good point it doesn't need to be at 2500 rpm to watch the rotor phase being only dependent on the vacuum advance.
I will get started on this first thing Saturday morning and hopefully have myself an engine that's miss fire free before the weekend is over.
I see that Rick sells a modified reluctor online but he charges 35 bucks for it, seems a little pricey and I shouldn't have much of an issue making my own dowel pin slot on the reluctor with my drill and vice.
The miss firing got better when I turned the vaccum advance ccw which turns it down I thought? Or makes it require more vacuum to advance it.
So I'm thinking the rotor phase is too far ahead which is in turn cross firing to the cylinder ahead of the cylinder it's supposed to be firing, which makes me think I'm going to have to bring the reluctor back a little bit.
I still don't fully understand how this re-locating the reluctor changes the position of the rotor but I'm sure I'll figure it out. Does changing where the reluctor is mounted change where the distributor shaft is lined up?