I just recently change front and rear diff fluids. Notice led black marks on shaft coupling and bolts. After I was done I threw it into 4wd and it was rubbing like crazy. I have a 6 inch RC lift kit, and have had no issues. I plan on contacting the shop who installed kit, but was hoping some one out there has experienced this, or has a solution. Any info will help. 2010 F150 xlt 5.4 4x4