do you have a 2 door or 4 door? if the latter you will only need a new front drive shaft with that much lift. if you have a 2 door you will need both front and rear due to the angle of the DS on a 2 door.
edit- here is some extra info from the noobie thread
http://wayalife.com/showthread.php?...s-Every-Newbie-has-about-the-Jeep-JK-Wrangler
Q: What are all the components that I will need with a 4" lift?
A: For a 4" lift, you should have a set of 4" coils, bump stop extensions, longer shocks, extended brake lines, longer sway bar links, adjustable front track bar, adjustable rear track bar, front and rear track bar relocation brackets, dropped pitman arm, adjustable upper and lower control arms front and rear and new double cardin u-joint style drive shafts.
On a 2012-Up, you will want to install a new front drive shaft regardless if you have an automatic or manual transmission. Assuming you install new, longer shocks with your lift, the extra droop you will see at a flex will cause the slip shaft boot on the drive shaft to tear. However, that is just one problem you will encounter. Even if you install exhaust spacers or relocate the cross over, the CV boot at the output shaft will be sitting at a significant state of pinch and this will cause it to fail prematurely.
Q: Are new driveshafts needed after installing a lift?
A: You really should consider installing a new rear double cardin U-joint style drive shaft if you have lifted your Jeep JK Wrangler 3" or more and have a 2-door. This is needed because the short rear drive shaft of the 2-doors will be at a steep enough angle that the CV boots will wear out prematurely. However, in order to do this, you will need to buy a set of rear adjustable upper control arms so that you can properly set your pinion angle. 4-Door Unlimited models do not have this problem as their rear drive shafts are very long and a lift will not effect the angle of it too much. As far as the front goes, if you have an automatic transmission, you will need to replace the drive shaft with a double cardin U-joint style unit as well as the diameter of aftermarket shafts will be considerably narrower and will not come into contact with the transmission and/or skid plate. Failure to do this will result in the tearing of the factory drive shaft boot as it makes contact with the transmission. Manual transmissions will not have this problem and keeping the factory front drive shaft will not be a problem.
NOTE: On a 2012-Up, you will want to install a new front drive shaft regardless if you have an automatic or manual transmission. Assuming you install new, longer shocks with your lift, the extra droop you will see at a flex will cause the slip shaft boot on the drive shaft to tear. However, that is just one problem you will encounter. Even if you install exhaust spacers or relocate the cross over, the CV boot at the output shaft will be sitting at a significant state of pinch and this will cause it to fail prematurely.