driveshaft is binding up. For reference, this problem only started when I switched from the stock two piece drive shaft to the one piece Z1 Platinum. I think old mount (tranmission) were not worn enough to cause this problem to show up with the the two piece, where as it is with the one piece. Also, if I roll into the throttle smoothly there is no problem only when I just press the pedal to the floor does it seem to shutter. Keep in mind that with the new transmission mount, this effect is dramatically reduced but still slightly there.