Vibrations while driving.

I am experiencing shaking or vibrations while driving usually over 40 mph to about 65 or 70 when the let off the accelerator it seems the shaking gets worse until the vehicle slows to under 40. I had taken the car to a Firestone to have a visual inspection done and it was said that it needed rear brakes and rotors and a rear wheel hub assembly on the right side, they said the cause of the shaking was the rotors. Since then I have had the wheel hub installed and rotors on both sides but not the brakes replaced. The vibrations are still occurring... What could the possible cause be? Also the steering wheel has vibrations in it also but not during braking.