Hi, recently bought a brand new A4 Black edition - Automatic 35tsfi model. noticed slow acceleration, engine revs high when changing gear. 
phoned Audi dealership and they advised to contact Audi Roadside Assistance.
Roadside Assistance came out and did a diagnosis check and 6 mile road test and found no faults and said vehicle was okay

Since then car now appears to have more acceleration, but engine idle is more noisy and slight vibration in the engine and car

 

 

 

I used to have an A5 35 tfsi and noticed something similar:

When I wanted to overtake I would press the throttle, it would slip into neutral, rev like crazy, then eventually pick a gear to allow me to overtake. assuming of course by that time it was still safe to do so. The accelleration was decent enough when it finally got around to it though

I just put it down to it being a detuned 40 tfsi