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.

I have an '02 Bonnie.

The Svc Mgr said he will try changing the tires to Michelin for the vibration. I noticed another post where someoone said that the entire steering rack was replaced to fix the clunk, clunk

So are you still under warranty? I just had the steering shaft replaced and had them look at the vibration at 65mph issue. They claim it'* because 2 of the tires are "bad". They did spend a lot of time re-balancing and stuff. I must say it'* gotten rid of most fo the problem. I can live it at this point until I have to buy new tires.

Now here'* a thought: since I also had the steering shaft done at the same time, could that have caused a vibration maybe? Replacing that shaft made the whole car drive 100x better........I wonder if it'* related.....