Problem with my car that can't be diagnosed. A little over 60mph, the front end starts to vibrate. Started after getting new rotors put on. I've had the rotors re-mounted, new front wheel bearings, new control arm bushings, and two new front wheels. Guess what? Still not fixed! The vibration is less intense now but still present when you hit 65mph.
Guess you can't expect much out of a Chevy.