Re: drive line vibration----has truck ever been wrecked? is it 2wd or 4wd? from your email it sounds as though you have isolated the vibration as coming from the rear end. But if you arent sure, you may need front wheel bearings and/or a set of shocks all around. When the vibration is at its worst (around 60mph or so) note your tach rpm speed. then downshift and bring the engine speed to the same rpm. if the vibration occurs at the same engine speed no matter what gear the tranny is in, the driveshaft is not at fault. if vibration calms down or stops when tranny is in different gear but at the same engine speed, it might be 1) bent driveshaft 2) dirt or whatever clinging to the side of the driveshaft to make it run out of round 3) driveshaft out of balance. any weights missing on the driveshaft? if not, pull the driveshaft and reinstall 180 degreees from original position. if all else checks out, are your motor mounts ok. good luck, let us know what you find.