I wonder what the difference is between the rear suspensions of the '05 QC's vs. the '06 QC's, that causes a vibration to show up only in the '06's? A difference in the drive shaft center support bearing location maybe? From what I have heard, the frames on the '06's are from the 3500 series of pickups. Maybe the leaf springs mount in a slightly different location, or the rear axle mounts at a slightly different angle giving the drive shaft a different angle? Are the shock mounting locations the same? Anyone have any thoughts on this?:dontknow: