I had 4WD issues similar to what I think you have. In the end the transfer case shift motor needed to be replaced, but before I figured that out, I kinda had it figured out how to get it out of "4WD" at least to a point where it would drive (need to get to work). The rear diff would still be locked, but from what I could tell the front wheels were not powered, at least until it would randomly slide back into 4WD.
Anyways, technique for temporary non-4WD:
required tools: wrench, legs, 15minutes of spare time
-Park Expy on a hill facing down hill. (not too steep, but enough to get it rolling)
-trans in neutral
-set parking brake so car doesn't roll down hill
-turn off car, pop hood, get friend to sit in driver seat in case it rolls (optional)
-disconnect battery, go sit in car and watch netflix for 10-15 minutes
-reconnect battery.
-double check 4WD selector in 2-Hi
-turn key to on, but do not crank/start motor (all the accessories, hvac, etc should come on, but the brakes and steering will remain unboosted)
-release parking brake
-car will roll down the hill, let it go for a little ways (<5mph seemed to work) only need to go ~15-30ft in my experience.
-stop car (depending on momentum, you might need help from the p-brake since the regular brakes are unboosted)
-trans in P
-turn key all the way so the engine starts.
like 70% of the time if i went through all the steps this would pop it out of what the car believed to be 4WD-lo/4WD. Sometimes it wouldn't. This is the result of googling and reading forums and trial and error. Judging from other's posts on various forums, it will also work if your tcase motor is fine, but the tcase is just a bit stuck from lack of use or whathaveyou. I have no idea why this worked, and it might be a bad idea, so please attempt at your own risk. Really though all of my issues cleared up once I replaced the tcase motor. The above was only a short term bandaid, obviously not a real long term solution.