The driveshaft length isn't causing the rear tire to rotate backwards an inch when you step on the Jeep. But with you guessing it has 4" of lift are you having any drivetrain vibrations? Is your transfer case skidplate dropped down from the frame with spacers which is done to stop/reduce vibrations?
To know for sure what suspension lift height is installed measure your front and rear rear spring heights. Stock up front spring height is 12", 8" in the rear. Any height above those numbers is your suspension lift height.
Show us a photo of one of the body mounts between the frame and body, we can tell you how much, if any, body lift height you have.
With 4" and taller suspension lift heights it's time to install a slip-yoke eliminator (SYE) kit and a rear DC (double-cardan) driveshaft. That gives more room for a longer driveshaft and reduced drivetrain angles to eliminate vibrations. That modification also requires adjustable length rear control arms so the pinion angle can be set properly for the DC driveshaft which requires a different pinion angle from the OE driveshaft.