I just put a six in lift on my 81 K-10 and finally got to run it in 4wd, and noticed a problem. In 4wd, when I get on the throttle there is a rubbing sound coming from the X-fer case. When I looked under it I noticed that the upper U-joint was rubbing on the cross member. Only when I romp on the gas. When I was putting around it worked like a champ. Is this a common issue, and if so how can it be fixed? Thanks for any help.