I have had trouble with my A6 4.2 automatic transmission for about a
year and the dealer can find nothing wrong.

Intermittently when I accelerate from a dead stop the transmission does
not deliver adequate power.  Engine revs are appropriate for the speed
but it feels like I have started in 2 or 3 gear.  There is just no
acceleration.  With mild accelerator pressure the engine revs to 4000
then abruptly shifts to second.  Power is then OK.  If you really need
to you can push the accelerator hard and it like shifting down from a
higher gear.

This happens both when the car is cold and when it is hot.

The dealer has had it three times and finds no codes from the
transmission and they keep having me drive a mechanic around but of
course it won't happen then.

I am leaving it at the dealership this week and giving them permission
to drive it until they experience the problem.0

Anyone have any ideas what may be the cause?