Hi,
I am also interested in the average consumption of the 3.0 M54.
I've got a M54 3.0 AUTOMATIC. When I bought the car, the fuel consumption was 8.9 to 9.5. Even if I pushed the car hard, it would go up to 10, but then come down again.
I then replaced the battery and it read 12.0, but is now slowly down to 11.0. I hardly drive the car hard.... usually just cruise along at about 3000 rpm.
I think this is very high, and I posted about it here, but since I don't do a lot of mileage I haven't been that concerned about investigating it further.