Irony sucks doesn't it? I recently had this happen on the WJ I owned. Is that the ACTUAL track bar you own? If so, I am betting that is where your problem is. It could be one of two possibilities...
1. No matter how tight you have made the track bar bracket, once under load it is finding a bit more movement. There has been enough corrosion behind it that it has extra space in places that should be against the sub frame. Solution-- Weld it to the frame.
2. If that is the EXACT track bar you have, then its likely that the poly bushing is bad on the one end. Its hard to tell by horsing it around with a pry bar, but I can almost guarantee that is your problem. That track bar is a JKS track bar (that is what Kevins Offroad sells), and Kevins Offroad actually offers a heavier durometer bushing for that style because many folks with WJ's have had this problem. This new bushing is the closest thing to STEEL that any plastic can actually be. You can hardly dent it with your finger nail. Get that bushing, and it should fix that problem. Keep in mind, the new bushing is TIGHT AS HELL to get in, but it works. If you have poly bushings on BOTH ends, then replace them both. Let me know if you need help sourcing these. Look under the WJ stuff on their website and you should be able to find them.
I had crappy tires on my WJ, and I hit a bump wrong and got death wobble. Once it happened it kept on happening because it wallowed out the track bar bushings enough to create space. You may have had another problem that initially caused your death wobble, but since it happened once it was enough to "make room" in the bushings.
A.