I went to the track yesterday ran a best time of 13.07 at 107 mph before eliminations where I dialed in at 13.13 had a .010 rt and ran 13.19 lifting before the finishline, got a bye run into 3rd round when the trans got stuck in 4th gear and the shifter would not move. I think I broke or bent the shiftfork for the 3rd and 4th gear shift. I was able to jiggle it back into nuetral and now I can use all gear's but 4th or it get's stuck, but it fall's out of 3rd if I don't hold the shifter in place. I've heard that the shiftforks are made of aluminum in this trans. I don't know for sure that this is the problem but I'm going to look at it further Monday after work. Who is the best to go to for a high performance/Race overhaul on the T56 and how Much does this usually cost to have done. I may fix it myself but I don't know the trick's that are done to make these tranny's stronger and perform better. If anyone can help with any tip's on what should be modded and who is able to do a high quality/performance rebuild I would really appreciate it!

 

Mine did the exact same thing. Ended up being the keys on the 3/4 slider had broken apart. Whether its the keys or a shift fork it still involves tearing into it. I'd suggest billet keys for the 3/4 slider, a steel 3/4 fork and bronze fork pads. Might as well do syncros and bearings while its apart.
I've never done a tranny before and was able to do it myself without much difficulty. If you've got the time I'd suggest saving a few bucks and doing it yourself. Lots of little snap rings though. A press is helpful too.
I got all my parts at t56rebuilds.com
good luck.