Originally Posted by Bajaman

This is a little difficult to follow (who said what), but I'll add my two cents. When I first did the swap, I had the normal vibration (1700-2000rpm) in 3rd and 4th. I tried lowering the rear x-member, I now have the proper x-member. Neither substantially affected the vibration. NOW, I have increased the output of the motor considerably with the addition of a VNT turbo. I have also put in SD265 nozzles and adjusted the timing to 26*. With all of these mods, I now have 'bucking'. This can occur anywhere from idle to 2000rpm. This is low frequency say ~1Hz, and only occurs under light load. I have been contemplating adding weight to the flywheel, as it is becoming unbearable. I agree that the flywheel mass is definitely a factor and I will try adding ~20lbs when I can get a flywheel.