Pulsing vibration at around 55-65 mph

[GMC Guy]

Originally Posted by nbpro

I have seen tires do this. The steel belt be worn out. Maybe somewhere to start looking.Torque Converter exhaust mounts allso

really? the tires are only a couple years old with like 85% tread. 275/60/15 bfg radial t/a's

[PRattenbury]

You could certainly have a defective tire with a bad belt causing a vibration. But typically a bad belt like that can also be felt at low speed. If you jack up the back wheels, start it up and put it in gear to let the drive line work while you watch, it may become obvious what the problem is if you look at the wheels, if you have a center bearing in the drive shaft check it out, and if all else fails, be ABSOLUTELY SURE the vehicle is stable and safe on the stands. Tape a piece of chalk to a screwdriver and go to the rear of the driveshaft. Slowly bring the chalk closer to the driveshaft till it touches. Do the same at the middle and forward end of the shaft. If the driveline is straight the chalk will leave a continuous line on the shaft. If the driveline has runout in it, the chalk will touch the shaft in one spot, but not leave a continuous line. Whatever you do, though, please, BE SAFE.

[GMC Guy]

i guess i'll start with having the wheels re-balanced lol

[white82]

Originally Posted by GMC Guy

really? the tires are only a couple years old with like 85% tread. 275/60/15 bfg radial t/a's

if they sit at any point for long time.. the tire can create flat spots.. thats why u see people putting there classics on jack stands in the winter..