It's either bad U-joints or improper use of the 4wd.. The only time you should use 4wd on pavement EVER is if you have a 242 Transfer case, with the shifter in the 4FT position. If you have a 231 case you should NEVER use 4wd unless you are on slipper road surface, ie dirt or snowy street.
96 XJ 4.0 / 231 / 3.5" JY Lift/ 31" BFG /.....
93 VT1100 - Harley killer.
97 ZJ 4.0 / 242 / Stock
93 ZJ 4.0 / 2"BB / Wranglers / RIP-Gone but not forgotten.
If it aint dirty, it aint a JEEP, it's just a SUV.