I have the GS 10th anniv. edition also with the OZ rims..my also shakes the same way at about 55 and up I had the tires balanced and rotated nothing changed... but on mine I also hear a humming noise coming from the right front when going strait or right but slight left turn of the steering wheel it goes away..somone told me it might be the wheel hub bearing...im gonna check this week on a lift move the tire holding it on top and bottom to see if it moves in and out from the car...somone said this is the way to check.