One thing that might have made a difference there is the fact that the Cummins power numbers are up to 10k ft above sea level. This has a lot to do with the turbo calibration, but it makes restrictive at lower altitudes capping power output.
I am not sure what altitude the Powerstroke or Duramax are rated up to and may loose power as you go up. Although this would not matter to much on a wide open run from a dead stop because the Aisin shifts so **** slow that the Duramax would be long gone by the time the it finally gets up to speed.
