Still trying to figure this thing out, changed oil from the amsoil syn gl4 to Pennzoil synchromesh and now currently have old school 80/90 gear oil, problem is I can't seem to find 80/90 that is only gl4, the one I have is gl4 and gl5 rated 80/90.
Almost seemed like the old school 80/90 was a bit better, but just came back from a stop and go drive and a good highway run in about mid 80's degrees day and it seemed with the car getting warmer than usual it was hard to get into first or any gear actually, so I tried like was suggested here was to shut the engine off while trying to put it into 1st with the clutch depressed, it went into 1st as soon as the engine was shut off.
Not sure where to go with this S--T. appears as the whole powertrain gets hot/hotter and all the parts expand it makes the going into 1st more of a problem. Don't even know where to look anymore???

Sounds like the clutch disc doesn't have enough clearance. Take the inspection plate off. Have someone depress the clutch pedal, and you put a feeler gauge inbetween the disc and the pressure plate and/or flywheel. You should have at least .060" gap. If you do not, adjust until you do and then go retest the vehicle. Pretty simple 15 minute test.

Just checked the clearance with the clutch depressed and its well over 60 tho, the disc flops around and will slide back and forth on the splines so it's not hanging up at all, not sure?? seems like I said before if the trans is not cooking hot its fine, just ordered up some of the sta-lube sl24239 gl-4 trans oil that Brewers recommends, gotta keep trying to figure this crap out!!!!
Thanks all for the suggestions, keep them coming.

Here's what I would try at this point.....

I would want to try and determine if the disc/input shaft is turning, when it's hot and the clutch is depressed.

Go out, drive it around, get it hot to where the problem is occurring.
When you get it back home like that, immediately jack it up and get it on some jack stands or lift(or if you have a friend with a lift, etc).
With the inspection cover removed and the motor running, brakes set, you should be able to see if when you push the clutch in, does the disc stop turning or not?

If when trying to push the lever into gear the disc doesn't stop turning........ Either there is too much drag on the input shaft in the bushing....... Or the brass ring just doesn't have enough friction to stop the gears from turning.

I put in one of the newer style roller bearings thinking that the old style brass bushing was causing this problem

I guess my thinking is...... The disc is either turning or it isn't.

If its still turning, I don't see how it can be anything other than something is creating more drag to keep it turning than the brass ring has to stop it from turning.

I was not going to do so but will ax again. Perhaps I have overlooked response.

What happens when going from neutral to either reverse or 1st gear, engine running.

Are you certain that clutch disc is not warped?

Still interested if clutch shaft pilot bushing or bearing is to tight or otherwise damaged.

Suppose it is possible that pressure plate not releasing equally about its entire perimeter,,,because of defective pressure plate, incorrect , improperly installed or damaged throw out bearing.

There was posting regarding clutch release linkage, has this all been resolved.

Adjust clutch to where no free play at all,,,,can you get into gear then?

How hard is it to get it into reverse after its all heated up?

I would think if the issue was excessive drag on the input shaft, then it would grind A LOT when going for reverse.
If reverse seems pretty normal, and you could get another gear(like 3rd or 4th) normally, then I would think there is an interface problem with the brass ring and cone for 1st gear.

What happens when you try to go from reverse to first?