did an engine swap.... excited about the swap so ive been driving hella hard...
wake up one morning and i cant get into reverse. ive been pushing my car out of the garage each morning.

1,2,3,4 all work fine....5 is hard to get into but still works. cannot get into 6th at all.
its a 99 usdm gsr tranny.

what is causing this? what can i do? rebuild whole tranny or buy an lsd? for anyone who helps me, thank you.