Originally Posted by gsmitty
Yes- I have had it on the fancy schmancy Hunter Blancer at the Dealer
I can't find where you said what year car you have. I have been through the tire question on the stiff and light unsprung parts problem. I picked a car with Michelins because they were "rounder" and stayed round in my past experiences with them. The service manager at the BPGMC dealer carefully rebalanced a second time ont he Hunter and got most of the imbalance out.
GM'* solution to problems on the Deville, Park Ave, was to put Michelins on if they didn't already have Michelins.
At 10K mi after driving it again and my observing when the vibrations at high speed came and went, he checked the alignment. Front was tweaked to center of range and rear was corrected on toe-in, which was off. The service manager started as an alignment specialist so he did the alignment himself. I t fixed the problem.
I realize your car has other symptoms. I don't want to irritate, but there may be more than one part to the shaking problem. Good luck.