I finally got tired of the excessive amount of vibration at highway speeds in my Deville. I had new tires installed with Road Force Balancing, rotors turned and brake pads replaced. I read through my Helm and found out that excessive rust on the hubs and the back of the rotor can cause vibration. I spent 2 hours cleaning the rotors and hubs with PB penetrating fluid and a large drill with a rust removal brush attachment. I test drove the car, and the vibration has been eliminated. Who knew a little bit of rust could cause that much problem.