Have the tires checked for balance, rotating them might shift the "bad" tire around but still a slight vibe is hard to track down without first eliminating the tires completely. If once they are checked its time to lift the jeep and start prying on upper and lower control arms and ball joints and tie rod ends looking for play. The jeep has to be off the ground, wheels removed and suspension floating, supported by the frame only. Don't forget to check track bars. Once all steering components have been check, its drive line and u-joints...fun fun.