Took the Jeep out wheeling last night, and I noticed that going up a steep hill in 4x4, the front axle jumps more than nomal, kinda like death wobble. It doesn't do it on flat ground, or down hill, only going up an incline. Anybody had this problem before?

 

Bad upper control arms can lead to excessive axle twist. I diagnosed mine by reversing down a hill quickly and hitting the brakes hard. Heard popping sounds and the axle twisted much more than my stocker xj. I also had my head hanging below the rocker panel while holding the door open during this test. Not an easy thing to do.

 

If upper control arm bushings are suspected, try this; On level ground, reverse jeep to walking speed and tap brakes, hang head out window while doing so and look for axle to shift or roll. Then do same in forward gear.
Can also examine the upper control arms at axle end for a very bad bushing, the bolt should be 'centered' in the bushing can.

Essentially what MonacaYankee said.