Go back to the truck and hook up with the key in the RUN position. Launch EFILive Tuning Tool.
Select FLASH->Program PCM Calibrations. You will hit start, and it will say the cable is not "married" to the truck. Close the FLASH window and try again, and there will be a new button on the window to allow you to marry it.
Now do it again, and in less than 2 minutes, you will have a pretty good tow tune that is essentially just a the GM data that has been moved around a bit.
taken from here
http://www.duramaxdiesels.com/forum/showthread.php?t=35