A833 Can't Downshift / Poor Performance

I think you've found your problem, but wanted to share a similar experience with shift issues.

Had a buddy who bought the whole 4spd conversion kit for his ebody as "new". Everything came in nice crates, and all the parts definitely looked like brand new OEM stuff.

We get the car together, and it won't shift. Did all the same dance with oil changes and trying to adjust every damn thing and replacing parts. Still shifts like trash.

Finally yank the trans and decide to see if we can spot anything obviously wrong. Got the side cover off and within a minute we had jammed one of the sliders. Couldn't get it back to neutral!

We go over to my used up, wore out core I hadn't yet rebuilt and immediately notice the gears are closer together at 3 and 4.

Turns out, his trans had a snap ring that was too thick. The one that holds the output shaft bearing in the tail housing. It didn't seat in the machined groove and the bearing moved when he tried to shift. The sliders were all fubar because the whole cluster had shifted back and so nothing would align except once in a random while. So we carefully sanded the ring down about .003" and it snapped in snug (took a few dozen tries, didn't want to go too thin! And had to keep it even).

Put it all back together and not a single problem since.

Probably unrelated, but I figure someone else will eventually have a similar experience and the info might help them when they go searching ;)