The driveline would make a rumble or vibration at hiway speeds when coasting. If I accelerated or let off gas noise was gone. I inspected carrier bearing and u-joints, all OK. Found spider and side gears had metal flaking off, put in chryo gear set and checked backlash. Problem was much better but could still be felt. Found pinion angle was -8. Truck was lowered with an X-Metal kit when I got it. I bought some spring perches and had them welded in today. I set angle at +4 1/2. I will finish tonight when I get off work. Going to try slicks next year and didn't want the rear end twisting on launch.