Vibration Through Car Starting at 40mph

[Exauray]

Hi all, I have just had a pair of new driveshafts fitted as my A4 Avant 1.8t felt like it was skipping across the road when turning corners. This problem has been fixed now but now when accelerating in a straight line I get a vibration that gets gradually stronger up to 60mph and then starts to disappear after going past this speed. The more power applied the worse it seems. The steering wheel doesn't wobble its literally through the car. It feels like going over a rumble strip on the motorway! The garage has fitted Shaftec drive shafts. They have balanced all 4 wheels and are now at a loss. I've read elsewhere that non Audi shafts can cause problems? Any advice on what to do next?

 

[pauldazzle]

Speed related vibration wheel balancing or a flat spotted tyres ?
Vibration under load in any gear I would suspect drive shaft failure.