Ok I going to solve this problem once and for all...I hope.

The only thing original on the truck since the old setup is the rearend and drop kit but playing with the pinion angle seems to change the vibration intensity.

Right now its set at maybe -1* on the trans/eng and the rearend is -3to4* pinion angle.

The vib is really noticable now at this setting at the speed of 65-70mph and the faster you go I guess the harmonics of it change and it smooths out.

Look at the crappy way DJM adj. pinion angle...