Most likely the collector is too small and way too short. The 2 inch primary isn't so bad, but the collector is small and too short which is typical.

Bigger primary - if you can do it without a tight bend at the port to make the turn.

By too short do you mean the merge section of the collector or the overall length? Does the exhaust add to the effective length of the collector?

i have wondered about the collector/exhaust relationship before as well.
if running same size tubing as the collector to an x or h pipe, does that effectively lengthen the collector ?
or am i not taking something else into account ?

The exhaust gas is looking for a change in area, in either direction: a step, collector, X pipe, even a really bad weld bead, whatever (but not a curve). Any of these cause a reflected pulse. If you're smart or lucky (I'll have to rely on lucky) the extra pulse "lines up" with an existing pulse (called superposition) at a useful RPM and enhances it. If not, it (partially) dampens it or does other evil things.
That's why the old advice "built some length adjustment into it" is still valuable.

I'm looking for some real world examples on whether my hoagie would pick up with bigger headers. Current combo in a 3500lb E-body...
528ci Low deck, 12:1 on E85, Indy SR heads Max Wedge ported by Modern. 1050 Dominator. The car is setup for a decent amount of spray with a fogger. 3.73 gear, 28" tire, 2.28 first gear 727. Cam specs: .816"/.799", 284/300 @.050, 114LSA. Current headers are 2" primary 3.5" collector Super Comps that were probably bought during the Reagan Administration. I plan to run mufflers.

WOW, gave up all the info here !!

I can tell you from my real world experience. I went from Pro parts 2" to a set I made 2 1/4 with 4" collector. Really didn't pick up.
Now after getting my engine Dyno'd at BES, he says whats holding it back is the LENGTH more than the diam. He told me 25" long primaries. (my current headers have 35 - 40" primaries, but its hard in an A body without going fender exits) And we have pretty similar combinations.
Also I cant believe you have so much starting line ratio...?

Haha! Well, I figured the only way to get good answers was with good info. Besides, the my junk is waaaay to heavy and down a few hundred HP to hang with you guys!
When you're talking collector length, is that the length before a muffler or including a muffler? I'm on the fence for fender exits. Half my buddies are twisting my arm to do it and the other half have threatened to beat my @ss if I cut the car that much. I'm surprised to hear yours didn't gain with bigger primaries. I know you're throwing some spray at it.
I had 4.10 gear with a stock 1st gear. That was plenty of SLR! Not sure if it could pull a Glide at 3500lbs???

collector length ? well if you plan on running a muffler I guess that would be included in the overall length. I would say go bigger if its longer. Instead of 4" consider 5"

The fender exits...Ughhh I really don't like them, but they are the way to a real short primary tube. Again you probably want 25-30" max. If you going fender exit im assuming you going to use a Burns type real short muffler? If under car then do what I did, Cut a cheap dynomax or similar straight through, I cut 5" off each end and ...there you go instant "shorty" mufflers LOL.

On the SLR, don't be shy. Im leaving in 2nd (1.48) and 4.11 out back.
I hate to say it but the trend right now is 1.40 or less and 4.30 or more. Works well with little SLR and a lot of gear out the back to pull the car through. Those 3.73 gears are lugging the car on top, but I know you got to work with what you got. Less SLR will always help with No Prep and junk tracks. If possible consider going back to the 4.10 or 4.30 and get a valve body that will allow leaving in 2nd. This also may require a stator change in your converter. Yes the powerglide could be a good option for you. It will also dump a bunch of weight over that 727...lots of stuff to think about

Do you have any racepak or data logger ? A sportsman racepak will give you so much real world info and help you see whats going on, it will eventually pay for itself in good decisions rather than useless testing. especially with converter and gearing...

you racing through the mufflers ? If so i would bet its a lot faster open headers ...youll lose a lot of weight, those flowmasters are heavy, and they really dont flow well either lol.

Have you tried tractor fluid in the trans ?