[bobcowan]

Before replacing any parts, spend the time and money to set up the suspension properly. You front and rear suspension is a good design, and should handle well at speeds well above 100 mph.

Start by setting ride height. I like 3.5" front and 4.5" rear. Disconnect the sway bars, and be very meticulous about it. Changing the height at one corner will affect the other corners. SO you spend a lot of time goi ng round the car checking and adjusting until everything is perfect.

Checking corner weights is great if you have the equipment. When the corner and cross weights are perfect, so is the ride height.

Then spend the time and money to get a good alignment. I suggest doing it yourself. You don't need much special equipment or special skills. It is a pretty simple process. It is a tedious job, though. Expect to spend a few hours the first couple of times until you get good at it. Doing it yourself allows you to try differant settings until you find what you like.

Vibration above a certain speed usually means a problem behind the transmission. Engine transmission problems are usually rpm related, not speed. As said above, have all four tires balanced. Could be any kind of suspension issue, or even a drive shaft out of balance.