im here trying to help a freind . he has a 1998 jeep grand cherokee, 4.0 6cyl, auto trans, w/ select a trac transfercase , all stock except for a 2 1/2" lift and 31" tires. we went out on sunday and found some small sandy hills to mess around on. the first hill we came to, his front wheels wouldnt pull or spin, 2wd only, i messed around with it a little, it dosent have a vaccum disconect type axel. the front drive shaft would turn, and both axels at the knuckles would turn, but the tires wouldnt spin, seems to me to be a hub problem right?? later that day when we were leaving we tried one more little bank and it seemed to work. we took it home, got it raised off the ground and put trans in "n" and case in low lock. i could turn either front tire and it wouldnt spin anything else. i could turn the front drive line and both front wheels and rear wheels would turn. i turn the rear wheels and nothing else turns, but the rear drive line?? transfercase problem or hub problem? im a toyota and chevy guy and dont know anything about jeeps, is there a common prob with these? any help would be great!

so nobody has any ideas??