My 2002 pontiac bonneville ssei supercharge has 85,000 with regular oil changes at gm dealership. It has developed very noticible vibration and hum that increases when I go faster. I recently traveled about 200 miles at 70 mph and the hum and the vibration were a lot worse. Acceleration is slow and the battery monitor show that when the car is idleing, volts decrease and also in idle, the car doesnt move when my foot is off the break (does not roll or gradually ease forward). I recently put fuel syetem cleaner in the tank, but it didnt help. Do I need a tune up? And if I do. How much should it cost?