Did you mark the drive shaft orientation?, Did you put all the crossmember tranny mount BS back in? The thing I found out was that the tail cone on the 3550 is lower than a T5 and the rear of the tranny needs to be shimmed up. that and if the car is lowered it throws off the DS alignment as well. My DS also hed thrown a weight so I picked up an aluminum one that and the shimmying cured most of the bad vibes. one more thing if you are using an aftermarket shifter there is no rubber isolator between the 2 pieces and that also transmits a fair amount of noise and vibes. hope this helps
