Hello. I am running into the same issue with an 05 Avalanche. Apparently the 05-07 alternators use a different charging strategy than the 7603 OS uses. Looking at the alternator part numbers and pin outs shows 2 pins vs 4 pins. I am trying to find a work around and have not had luck yet. I have been trying to find an xdf for the 618 os from 2005 but it is incomplete. Hoping someone here has found a solution they can share with us.