"If I run the truck up to 50/55 and then depress the clutch,
vibration must be coming from a bad u-joint/torque tube bushing/wheels or tires."At 50/55 mph I would depress the clutch and turn off engine.
If the vibration still exist you can eliminate the engine,flywheel and pressure plate as the source of the vibration.
The vibration then, has to be in the drive train tires, wheels, pretty much anything that spins.
Also could be a bent axle shaft flange.
Like if a rear tire of the truck smacked a curb and bent axle shaft flange.
Jack up rear axle and spin both tires to see if tires are wobbling.
I had a bent rear axle shaft flange and the only way I could tell if it was bent.
Was to clamp a dial indicator onto the leaf spring and place the probe of the
dial indicator onto the edge/face of the
Axle shaft flange (the round plate that holds the lug nuts)
Then, by hand, I spun the axle shaft flange.
The truck with the bent axle shaft flange.
At slow speeds, it felt like a bent rim.
At 55-60 MPH it had a vibration.
