I just replaced the transmission on my 1990 toyota pickup 4x4 manual. The transfer case shifter can freely move between 4 high, 2 high, neutral, and 4 low. However when i start moving or let go of the shifter it will move from 2 high to 4 high or 4 low to neutral. Any ideas?

 

if it was me i would pull the boot, pull the tcase shifter and take a look.

 

Another thing. I havent put the front drivetrain back on yet. Could this be causing the problem?

 

If by front drive train you mean the front drive shaft, it's not likely that its absence is the issue. The shift rails have detents with spring loaded pins to hold the rails wherever you put them. Either those have failed (broken spring) or the shifting mechanism itself is so worn that you aren't full engaging the gears and the detents, and then they jump out into the other position. Like Vec said, pull the top off and take a look.

 

alright now i got everything all buttoned up and low 4 pops out but everything else works.
Whats the deal with that?