If you have the money, I'd recommended going with a CV joint on the rear driveshaft, rather than lowering the transfer case. Whiile lowering the transfer case will reduce the U-joint angle on the rear shaft, that procedure has two disadvantages: (1) it actually increases u-joint angle on the front driveshaft, and (2) it reduces ground clearance, which was probably the point of the lift and bigger tires.

You will probably have to lengthen the driveshafts. To see if you have to, after installing the lift jack up the frame at both ends of the vehicle and put the frame on jackstands. The tires should not be touching the ground (i.e., at full droop). That will extend your drivehsafts the full amount. Having done that, measure and make sure you still have sufficient engagement of the splines on the slipjoints of the driveshafts.