The coil spring rear has trailing arms. When you lower the rear axle in relationship to the frame (a rear lift) or most any kind, you rotate the nose of the rear diff up, which changes the rear ujoint angle. You can correct this the hard way by cutting off the trailing arm mounts and spring perches and reweld them with the axle at the proper angle, or the easy rednek way, by ovalling out one of the trailing arm mount bolt holes on the axle so you can rotate the axle on the trailing arm, pivoting on the other bolt hole, until the pinion is again at the right angle. I'd then weld on a pair of washers to the trailing arm mount to "lock" in the new angle. Or you could install CV joints in the driveshaft in place of the non constant velocity ujoints...