But I did peg the 85mph speedo on my kid's Grand Marquis looking for another problem. It had completely shot shocks both front and rear pitched like a cork in the sea, mechanic pulled one out of the trash to show me, the shaft fell out of the body.

There was no vibration.

However, I suppose it's possible.

How old are your tires? What brand? Could a cord have shifted or could they have flat-spotted?

Rear Nivomats are $250 ea. at FCPGroton.com, FWIW. I've always been annoyed by the fact that my non-self-leveling wagon doesn't sit level without a full load. I suppose the $250 rear shocks would be even more annoying.

For suspension/balance/vibration problems I use a local racing shop that more-or-less specializes in Porsches. They don't mind taking the car out to it's limits to diagnose a problem.

-Punxsutawney Phil