Lift kit contents explained: http://www.bigredheep.com/Tech/suspension/lifts.htm
How does a TJ suspension work? TJ suspension 101 The Suspension on a TJ is a five link, coil suspension the five links are the 4 (2 upper and 2 lower control arms (Control arms are mounted to the frame and the axle the run almost parallel to the frame and keep the axle from rolling) The fifth link is the track bar, It mounts on the axle almost at the end of the the axle and the runs the same direction as the axle and then mounts to the frame. This keeps the axle tracking straight, or keeps it from moving to the drivers or passengers side of the rig. The other essential part of a TJ suspension is the sway bar. This mounts on each end of the axle and is u shaped and mounts to the frame. This keeps the body from swinging(rolling) too far either way when cornering. I have disconnects for this so I connect it on the road and disconnect it on dirt. All of these parts are on both the front and the rear axles. So to lift a Jeep all of these parts need to be lengthened or at least checked to see if they will still function if it is lifted. The other thing you need to consider is the drive line angle. A TJ with up to a 3 inch lift will work OK with a transfer case lowering kit. This will keep the drive line angles low enough that it should not vibrate. Once you go 4 inches of lift or more ALL of these parts must be upgraded. I ran mine with a 3 inch Full suspension lift for a year and it went great on and off road. Once I went 4 inch lift and full lockers it became a bit weird on the road, so it graduated to a trailer queen.