I have been talking to a 4x4 shop about installing my lift for me. I don't have the tools to do this myself. They are telling me that "Unfortunately you cannot shim the rear enough degrees with shims. To run a cv shaft correctly it needs to be at 1 degree below 0 at the rear differential compared to the shaft or you will experience pre-mature u-joint failure and possibly a vibe." Is this true? They want to cut off the spring perches and re-weld them. By the way I have a 2001 Cherokee and I'm installing a RE6030 3.5 inch lift with the Hack-and-Tap and the RE driveshaft. Can a shim be used or are they correct in saying that I have to re-weld the perches?