Yep the track bar is usually the culprit, compounded if its lifted and has worn components. I have had it on a ZJ several times. First time it was cured by a new track bar. I had a franken lift with longer springs and spacers, its was fine. Then I went to a Rubicon Express 4 and it hated the control arms and those spherical joints. Terrible death wobble. ended up putting rubber stock bushings in and it solved it. Certain wheels with too much offset or as Jerry said, wheels that arent round can cause it as well. I had two sets of tires at one time; 33's All Terrains which caused it and I also had 34 in swampers which I left on because it went away with them (the bias belted kind) Go figure. Lose components are a good place to start after the tires/wheels balancing and then the track bar is next. You can put your tire upagainst a curb and in park have someone inside the jeep turn it toward the curb and you can see if the track bar mounting points are flexing. Good luck!!