check the bolt (Frame side) of the rear pan hard bar (ie trac bar) if you put a drop bracket (most likely came with the lift kit) some time the bolt strips in the drop bracket making the bracket move ie makes the rear end jump around, if a an offroad shop looked at it I would start there as well as follow the other posts advice

98 wrangler 2.5l 3 inch rustys, 2 inch body, 33X12.5 MTR's DETROIT LOCKER, 4.88 gears, moser axles, Dana 44 (rubicon housing)