Changed my friend's 06 silverado 4x4 L33 over to a 04 pedal and tac module so we could use a 7603 tune on it. Used a spare p59 ecm I had on the shelf to put a light transmission tune on it for now. After putting in the new computer and associated parts I am getting an alternator not charging message on the cluster. I checked the battery with a multimeter and I am getting a solid 13.2 charge at the posts while running. Does anyone have any idea if the 7603 tune could be causing problems with the bcm to cause an issue?