While I don't have a TJ myself, I have three friends with TJ's and my dad own a TJ. They all have lifts, the maximum amount that we have been able to go was three inches. This is with out adjustable lower control arms. One of my friends was running the Teraflex three inch with two inch spacers and the Flex arms on the bottom. He was able to adjust the pinion angle so that the vibration went away. (Note that he did have to put the transfer case skid plate spacers in to help the angles of the rear shaft.) Another idea is to check the u-joints for wear. My friend had a 97 TJ with a two inch lift and after about 50,000 miles the u-joints started to wear out. This caused a bad vibration and replacing the u-joints fixed it. Hope this helps.