I have a 2003 Ford Galaxy Auto Diesel. The whole car shakes badly at around 40-55m.p.h. Only when I press the accelarator. When I take foot off the accelator or put in neutral the car is fine. Only by pressing the gas I get the car to shake. I have got all wheels balanced and tracking done. I have taken to a few garages they can't diagnose it. Any advise is welcome.