ADMStunna- I have the same freeway speed vibration problem that you're talking about. This problem is far more pronounced when I brake lightly at freeway speed, causing the car to "shudder." I don't think it is a case of warped rotors, because I don't feel pulsation in the pedal, the steering wheel just vibrates more violently on the brakes. Anyway, I went to the dealer, and they balanced and rotated the tires, however only one of the tires was out of balance, and only by 10 grams--not enough to cause this vibration according to the tech. It was apparent, however, when the wheel was rotating on the balancer machine that the tire was out of round, or flat spotted. This seemed to be the case with all four tires, and the tech said that they've had some problems with the Advan tires becoming flat spotted when the cars have sat for long periods of time at dealers, or during transport to dealers. I think the problem is probably the tires, and I am wondering if anyone has tried to get Mitsu to replace the tires under warranty because of this flat spotting problem. BTW, my car has done this basically since the first time I hit freeway speeds, so I don't think the problem is any fault of my own.

 

That freeway speed vibration could be a symptom of uneven tire pressures. I had that happen to me before, so I re-aired my tires back to spec (I noticed they were off), and now the vibration is gone.