Trans experts! Here's a challenge for you...

[sadil340]

Weird , at least we are onto figuring it out good or bad .
do any of the shafts have excessive end play / bad brgs or bushings ?

The input shaft moves around a bit but I was told that it uses ball bearings so that is normal. The tailshaft seems pretty tight. We haven't broken the trans down yet to check inner shafts but that may be a strong suspect. The fact that acceleration causes the problem tells me it's something causing the gears not to line up properly but that's just a guess.

[Chryco Psycho]

the front shaft will move side to side a little but should not move in & out at all .
 what type of shift / side cover do you have , the double level or the ball detent ?

[sadil340]

Good to know, it doesn't move in and out. I believe it's the double level type - there are two levers for the detents. Is that what you mean?

[Chryco Psycho]

is there a E clip on the outside of the shift cover ?
If so it is the doulbe lever interlocking both shift forks

[sadil340]

is there a E clip on the outside of the shift cover ?
If so it is the doulbe lever interlocking both shift forks

No there are only the fittings where the linkages bolt on and the cover attachment bolts. No clips that I could see...

Here are some shots of the B-Body cover, it's the same design:

[Chryco Psycho]

Ok the alum cover retain the pin for the lever with a snap ring , the steel cover doesn't

[sadil340]

Well I'm done. Moving the linkage cover around does change the shift behavior but doesn't fix the problem. I'm throwing in the towel and buying a rebuilt trans. If down the road I figure it out I'll post the answer.

Thanks everyone (especially Neil) for your helpful suggestions!

[4 speed fish]

I pulled my tranny 4 times before I waved the flag,bought a new one and all is good.

[Chryco Psycho]

I wonder where the issue is ?? it could just be worn out .
 Glad I could try to help anyway 

[sadil340]

I pulled my tranny 4 times before I waved the flag,bought a new one and all is good.

I hear ya! Can do it in record time now.