Reasons for deceleration vibration

[Dan/Kzo]

When the cold weather settles in I would like to investigate and correct the vibration my truck has when decelerating. It is a pretty good vibration/rumble when the foot comes off the gas pedal. I am looking for some pointers and advice on what to check or recheck. Some history...Last year when I installed a rebuilt engine I dial indicated the flywheel housing with horseshoe shims in place and found .005 variation (which I felt was acceptable and better than what I removed), removed the transmission and installed new bearings, and verified the condition of the ujoint, which was tight as new. Transmission gears are not noisy and it does not slip out of any gear. This same vibration was present with the old engine and flywheel housing. It runs and drives smooth on acceleration and all driving speeds, just more rumble vibration than it should have when letting off the gas. I have other A's which are not like this. Any tips are appreciated. Dan Cargo