i have replaced u joint on my driveshaft(diif. end), tail shaft side's fine, jacked the rear of truck, speed her up to 50 mph and still vibrates, this will happen in 4wd or not(no difference). put rear tires to front and front to back: no difference. I looked to make sure front driveshaft's disengaged when t.case lever is to 2H, it is free. I have no lift kit on truck either. There's a bit a play in both upper ball joints, one bad axle passenger side(clickin) and a minor play in tail shaft to t. case but no oil leak... im running out of ideas, what do I check now?