at 4" need new control air and springs do not just work.
also at 4" if you have a front drive shaft that is rezzepa (boot on TC or diff end) will need a new one or it will blow up on you.
for a 4" lift i would also recommend
-upgrade to MX6 or bilstein most other will give you a harder ride
- a bigger sway bar in the rear to help with body roll. so upgrade to the addco 1" with grasble bushings.
- adjustable track bar for JKS, and longer end links in the front
-if u offroad get quick disconnects for the front
i will say go over to jeepforum.com and read up on lifts since there more about lifted jeeps then street jeeps over there
this chart tells you what u need