'96 Ranger 4WD Problems

My brother has a '96 Ranger ext cab 4wd, 120K with push button and auto lockouts with the 3.0 V6. He was having trouble with it shifting in and out of both 4low and 4high, and it eventually wrecked the transfer case. The transfer case was rebuilt, and upon being reassembled would shift in and out of 4high, but would not shift into 4lo. Our mechanic, for whatever reason, thought it was something in the front end. Upon tearing it apart, nothing appeared to be wrong. He went ahead and put new lockouts on, manuals rather than automatics, and still the same thing happened. He has given up on it, and $1,000 dollars later, the truck has a rebuilt transfer case, new lockouts, and only 4hi. My brother did manage to get it to shift into 4lo, but he said it took lots of messing around before it would do so, AND once it was in, it took him over 1 1/2 hrs. To get it to come out of 4lo. I am thinking it may be an electrical problem, but I don't know enough about that system to start tearing apart without some guidance. Any advice, tips, or solutions?