Ive had my XJ death wobble come and go, first it was an unbalanced tire after I slung the weight off on a trail, bad steering stabilizer, at one time I even had so much mud in the rims after hitting the mudhole that it threw my wheels off balance lol but basically just check everything and make sure its all still nice and tight and the rubber bushing aren't cracked/worn really bad. Re grease all the grease fittings in the front suspension, check to make sure your shocks aren't blown out, and make sure all your tires have weights on the inside and outside of the rim. Last ditch effort is just have an alignment job done, if there's a part that needs to be replaced you can guarantee the shop doing the alignment will tell you about it lol