I've searched for this and couldn't quite find what I have going on, so apologies in advance if I missed something.

The 2-3 shift in my 67 Coronet's 727 has become kind of slow under heavier throttle. It doesn't flare, it doesn't hang, it just kind of sliiiiides from 2nd to 3rd over maybe a second or a second and a half. 1-2 is fine, and 2-3 doesn't feel strange when I'm driving like a normal person.

I last had the pan off about 5 years ago to throw in a B&M 10226 kit and did all of the band adjustments you usually do when you have the valve body off. Not entirely sure how many miles have passed since then, probably around 10k at most.

I have a Lokar-type cable instead of the old linkage - it is adjusted out to have full pressure at WOT.

I couldn't find anyone describing this particular behavior, only people with shift flares or with this behavior only when the trans is cold.

Should I just start with a fluid change (it's not a ton of miles, but it is old) or a filter/full band adjustment again, or am I more likely nearing the end of some friction material's life?

Start with the fluid, filter, and band adjustment. it sounds like low pump pressure might be the problem, and the filter would be the 1st thing to do.
You have not given us any idea how many miles are on the trans itself, it may be time for a rebuild. 100,000 - 125,000 is a lot of miles on the 67 drivetrains. Most didn't expect the vehicle to make it 10 years or 100,00k miles, the ones that did were truly rare. .

You're saying a "normal person" doesn't use heavy throttle? Problem is likely the front clutch, worn sealing rings or clutches worn.

i do not like those lokar cable kits.
in my opinion, after adjusting many, then removing them for some other type of linkage, they are junk.
chintzee brackets and cheap bicycle cable that stretches, causing adjustments to vary are my primary peeves.
if needing a cable kick down, look into what mopar used on the later dakotas [?] or magnum pickups.
a MUCH better design, and one that works as it should.
just MY opinion. your mileage will vary..............

This one has 131k, so I was half-anticipating having to do that later this year. I do see some clutch stuff floating around on the dipstick, though, so maybe a filter will buy me another year or two.

The longer you drive it the more it's going to cost. Hard parts cost more than a simple rebuild. A very good trans builder once told me that the first time a trans doesn't feel right çall a tow truck. Do not drive it until it won't move any further.

I flippin hate LOKAR cables, absolute junk along with their shitters

if you're seeing clutch material in the pan on on the dipstick it's time, actually overdue

If you are really lucky, the filter change may buy you a few months at the cost of a more expensive rebuild, but at 131K, you are probably past an inexpensive rebuild anyway. Seeing clutch material floating around on the dipstick means the trans needs to be rebuilt now. You have used it up.

If the filter is plugged the friction material ia already toast. .
Doug

if i said what i really thought about that stuff, i would more than likely get a "vacation".

I found the filter wasn't actually plugged with loose material, it looks like I broke a single plate some time ago when I locked up the rear tires with manual 1st engaged a year-ish prior. The little chunks got partly pulled up the pickup tube. I think I will be fine for one more summer of chuggin'. I'm only running a stock Magnum 318 with a carb conversion so I'm not asking much of the trans right now.

I will come back crying if you all are right

Given I need to rebuild soon either way, what components are reasonable to upgrade in a '67 TF that only sees street use? A lot of kits I've looked up say they are only intended for '71 and up, which I understand are when they added a lot of Hemi-grade improvements to the whole line or something to that effect. Should I just get an entirely newer 727 or 904 instead?

If you are really going to try to squeeze a few months out of it, refill it with ford ATF.

Years ago I bough a very cheap an old Dodge wagon. We used it to drag our dirt track car to the track (a couple miles from home). One day it wouldn't move. I dropped the pan, replaced the filter and adjusted the bands and by my transmission guy's advice, put the Ford fluid in it. The old wagon did the job all racing season, that last week was pretty questionable, but it got the job done. I scrapped the old wagon, the transmission wasn't its only problem.

A 1967 318 powered car with a 727 that is only street driven only needs a stock rebuild. The 1st round went 131K miles in 56 years, do you expect to put 131K more miles on it?
The only upgrade that i would consider might be the part throttle kickdown, but I think you need a newer valve body to do that.

i'm not completely sure, but i "think" the part throttle kick down assembly can be installed simply by bolting on the assembly in place of the flat plate covering the 1-2 and 2-3 shift valves.
of course this assembly will not fit pushbutton valve bodies, but i'm pretty sure this can be added to 68 and up units.
perhaps JK will chime in and clarify this.

that was what i was thinking about.
thank you John.

Hard to say as there are several places the fluid/pressure can be lost going to the high gear clutch.
The drum to pump sealing rings, the front servo leakage, drum piston seal, number of drum springs, clutch pack clearance, even front band lever ratio plays part in the timing.
That dosen't even get into the valve body programming.