I just bought my 07 cts 2.8 two months ago. I just had new front brake pads put on it two weeks ago because I had the brakes looked at and they said that was all I needed. However when I am on the highway and hit the brakes at speeds above 60 mph my car and my steering wheel begin to shake rather violenly and it does not do this at lower speeds. I do have aftermArket 20 inch rims on the car that came with it when I purchased it. What could be causing this issue? Is it the large rims? Warped rotora( however I believe they would have told me when at my shop that I needed new rotors when they did pads)? Any ideas suggestions? Any and all suggestions r greatly appreciated. Thks .