Just recently I had the transmission fluid replaced on my 1997 A8. Immediately afterward, I started noticed that as I coasted (i.e foot off the peddle), the car would sort of "lurch" (as if it was shifting funny/hard into the lower gear). Passengers think I am playing a trick and tapping the brakes. Not so.

There is no noice and no RPM issues.

I suspect this is common.

My first thought is torque converter.