I had an issue like this, but my front drive shaft wasn't installed so I couldn't try in 4wd, but my issues was with the ujoints on the rear drive shaft, apparently it was allowing the shaft to bind up. I didn't think that would result in the jeep not to move forward or reverse, it was almost like the e-brake was set. Changed them then never had the problem again.
** I like Poetry, long walks on the beach and poking dead things with a stick..
91 Yj, auto, I6. (sitting in garrage waiting to be installed 4" RC suspension lift, swampers 33x12.5)
04 Chevy 'DirtyMax, stock