OK guys, I have 05 F-250 with the 6.0. When I back up and turn going slow, I can feel what seems like the rear end jerking. It almost feels like the U-Joints going out, but they are nice and tight. Also, when the truck is parked, I can turn the driveshaft almost 90 degrees beforw it hits something hard and stops. I tried turning my dad's one, and his doesn't turn at all. I tried a buddy's one, and his barely moves before stopping. What can this be?