2002 Volkswagen vibration while accelerating

I have a 2002, VW Jetta TDI diesel with 128500 miles. While accelerating above 60mph the front end shakes and the shaking increases with higher speed. I recently had a 4 wheel alignment and all 4 tires balanced also new struts and shocks. This did not correct the problem. I checked underneath the vehicle and everything seems to be tight. The vibration stops when I let off the pedal and coast.

I would appreciate some feed back. Thanks.

C. Smith