I have a 1982 Chevy Suburban with a 6.2L diesel engine and it has some strange issue with the driveshaft.

At highway speeds (55-65) the truck shakes real bad. It appears to get worse with speeds higher than 65, but the truck doesn't like to go much faster.

I replaced the driveshaft with a different one and appear to be having the same issue, although the vibrate is less towards the front of the truck now. Could is just be that both driveshafts were out of balance?

With the truck jacked up the old driveshaft moves up and down near where it connects at the rear differential. The whole "new" driveshaft moves up and down everywhere. This test was done at less than 10MPH with the rear wheels lifted up.

Any ideas? New U-Joints on the "new" driveshaft. (I put new in quotes because it was used and I just cleaned it up and put new U-Joints in it.)

I have a 1982 Chevy Suburban with a 6.2L diesel engine and it has some strange issue with the driveshaft.

At highway speeds (55-65) the truck shakes real bad. It appears to get worse with speeds higher than 65, but the truck doesn't like to go much faster.

I replaced the driveshaft with a different one and appear to be having the same issue, although the vibrate is less towards the front of the truck now. Could is just be that both driveshafts were out of balance?

With the truck jacked up the old driveshaft moves up and down near where it connects at the rear differential. The whole "new" driveshaft moves up and down everywhere. This test was done at less than 10MPH with the rear wheels lifted up.

Any ideas? New U-Joints on the "new" driveshaft. (I put new in quotes because it was used and I just cleaned it up and put new U-Joints in it.)

If the D-shaft moves up and down when connected to the rear diff it may be your pinion bearings.