First post on here, but have lurked for a while. I could really use your help for pre-planning Anyone know of a guide that gives detailed changes on the engine/drivetrain of the 8.1 by year? I know a little on the LD side, but the HD/8.1 is new to me. I have a 2001 crew cab 8.1L/Allison/4x4 that I am looking to swap a 2003 8.1L/Allison/4x4 drivetrain into. Reason being, the 2003 is a ridiculously low mileage drivetrain but is a beat-up regular cab. Curious on what changed from '01 to '03...reluctor wheels, sensors/wiring harnesses, fuel delivery, etc. Thanks in advance!