My truck is vibrating badly in 4th, 5th and 6th gears (G56). The vibrations compound with each higher gear, but I get no vibes in 1st through 3rd. The vibrations are most noticeable at 2000rpm and beyond. The vibes are not coming from the engine, it is smooth. The vibrations are likely coming from the driveshaft. I would automatically presume it is the U-joints, but any U-joint trouble I've ever had, has gone CLUNK, but I don't get any noises. What gives?

 

It's a u-joint or the carrier bearing. Drive the truck down the road and come home and park it. Climb under it and feel the u-joints. One of the endcaps will be hot. That is the bad one.

 

Are the endcaps going to be noticeably hot, since it is -30 here?

 

Any chance that it could simply be a driveshaft weight? If it is a u-joint, are there stronger, greaseable aftermarket versions?