Have you had the CCP done ?
also another thing Terry @ BMS has said this before
" We've noticed a lot of n63s throw a MAF sensor code at higher rpm/power levels. In some cases replacing the sensor with a new one has resolved the issue. The best price we've found is at rockauto.com BOSCH Part 0280218270, Mass Air Flow Sensor, $ 119.99. "
http://www.n54tech.com/forums/showthread.php?t=22748
Best bet is to read the code your getting with that drivetrain malf, that way I can help you out better.