I'm running the stock shaft with 4-1/2" lift (over 5 inches actual measurement). So far so good and I have tested it to full droop and the CV still has a couple of inches more drop left beyond what the shocks will extend to. You might have an exhaust clearance issue, but at 2-1/2 not likely. If you do, you can gain a little clearance with spacers, or get the aFe cross over pipe that eliminates the problem entirely. I'm running 2-1/2 degrees of caster and 3-1/2 degrees up angle on the pinion with no vibes. So with your lift I don't think you have any driveshaft worries.
14 JKU 4-1/2 AEV Dualsport RS, 37" KM2 on Pintlers, PR44, 4.88, ARBs .... under construction