Alright, I have an 03 Evo 8, 15x,xxx miles.
It has a ACT Performance clutch.

I just bought a new transmission from a fellow member. The tranny had been fully rebuilt, paperwork to prove it. After installation, I found I had no reverse. I put it in gear and as soon as I start letting off the clutch, it immediately grinds and pops into neutral. All my other gears are great. 1-5 shifts like butter. I talked to him and he talked to his mechanic that rebuilt it, and the mechanic admitted that reverse looked a bit chewed up but he didn't think it would cause any problems so he didn't do anything about it.

Could this be gear related or is there something else I'm overlooking? I've bled the clutch system, adjusted the pedal, and checked the shift cables and all looks good. I disconnected the cables and put it into reverse by hand and it still ground and popped out, so that ruled out cables. Could this be a clutch problem in any way or is it for sure an internal tranny problem?
I just want to make sure I rule out all options before I pull the thing again. I got another bad tranny with a bad 4th gear 2 months ago, so I'm kinda burnt out on pulling and installing trannys on this car..
I put the clutch in at the time of the last bad tranny that had no 4th gear, reverse worked fine with that tranny, so I don't think in a clutch dis-engagement issue, but I could be wrong.

Any help will be appreciated.

Thank you