Is this a new jeep or new lift?? With a new jeep or new lift the springs will be new and will settle in after a short time. The spring will break in and will sagg just a bit (they all do, its normal) but it shouldnt sagg so much that the rear oviously sits lower than the front. If it does, you can add-a-leaf which will stiffen your ride, or you can get slightly longer shackles for the rear. If carrying lots of cargo or a lot of towing it may sagg a bit more. Same solution though. If the jeep is new, I would take it back and have them put new rear spring on it, because a (good) new spring shouldnt sagg so much that the rear sits lower than the front.