Coolwater

Try this, take the driveshaft off the rear of the pinion flange and rotate the shaft 1 bolt hole. Replace the bolts and see if it got worse or better. If worse rotate it another bolt hole. This took care of a vibration I had similar to yours only mine is an automatic. A driveshaft shop told me to do this and I couldn't believe it would work but it took all the vibration out.