You may want to pull the rear output assembly and inspect your roller bearings and the 2WD/4WD synchro hub/shifter fork. You may also be able to check the front main bearing, after you get the rear assembly out by wiggling the main input up/down left/right. It should have very little play (1/8" - 1/4") and you shouldn't hear the bearings rattle. Try pulling it towards the rear, if it seems the bearing is slipping too far to the rear I would say the front retainer clip may have broken causing excessive end play making it hard to get 2WD. Don't be intimidated if the roller bearings fall out all over the place, wipe the oil out of the "pocket" they all go in inside the output shaft with a rag, and put them in with vaseline to hold them in place. DONT use grease since it has a much higher melting temperature than vaseline, and will prevent oil from reaching the roller bearings in the long term.
