1996 chevy lumina apv transmission trouble

Help I have a 1996 lumina apv I replaced the tranny 1 1/2 months ago and now the new transmission is shot too. I'm wondering is there something other than bad tranmissions that could be causing my problems? It seems to jump after you stop and there is no particular reason I could be on flat land or up hill. It seems to happen more when I shift in reverse, It does not stall out,although, will not move it will continue to run and start without fail. It will get stuck in what ever gear it happens to be in when problem occurs.

hi, i own a 96 sedan, same problem, mine you had to rev to get it to shift, oh it starts nicely, but then heats up, wont shift into any gears, it a 460t trannied they put in those, in the front of the trannie on the passenger side, is a little round thing, that is held in place with one bolt hanger, there is a vacum line running up to the exaust manifold, that part is called a vac m odulator, if you take it out and a little fluid comes out its bad, about under 20 bucks, it might help, also a friend of mine works alot on th em and he said he has fixed several of them with reinstalling the computer codes, since the trannie is control with its own seperate computer. hopes this helps, if you get yours running let me know what you had to do,, shur20k@yahoo.com.
ps, do you have problems with the visor clips, dam things wont stay in.