Going back to when I first bought this 95 Jimmy. I got it home on a tow dolly. It started and ran however there was a ticking sound and it sounded like it was coming from the transmission. I removed the torque converter bolts, slid the converter back and started it up. No ticking...
So down came the transmission and first thing when I pulled the pump; out came what looked like a*** Nail***. I've never rebuilt a transmission so I was a little apprehensive about taking on the job. I let a fella that said he worked in a transmission shop before rebuild it.
All forward gears work and it goes in reverse but it slips. Down it comes again after checking the reverse boost valve and adding the Lucas treatment.

Now this time there was no nail falling out after the pump. It was after pulling the input drum and removing the reverse drum that I noticed this rubber down in the reverse drum. It was down in between the spring and the clutches.http://i1137.photobucket.com/albums/...oncheck002.jpg
http://i1137.photobucket.com/albums/...oncheck003.jpg

Going to removing all the valve body bolts and removing the valve body I only counted 6 checkballs and noticed that there are no filters on the separator plate for the solenoids.
http://i1137.photobucket.com/albums/...oncheck001.jpg

After removing the separator plate I did see the check ball next the accumulator. I also noticed the check ball in the capsule at the rear had already been removed.
http://i1137.photobucket.com/albums/...oncheck006.jpg

The transmission was rebuilt not so long ago and the clutches look good.
http://i1137.photobucket.com/albums/...oncheck004.jpg

The band looks good too.
http://i1137.photobucket.com/albums/...oncheck005.jpg

I don't recall exactly which hole on the separator plate was missing the check ball but could this be the problem with the reverse slipping? Could it be the mystery rubber in the revers drum?