| Those are the RPO codes for the Duramax engines offered in different years of Chevy or GMC HD's. In the truck's VIN, the 8th digit specifies which engine you have. Only one option was available at any given time, so it's pretty easy, unless you have one of those spit years, like 2004
__________________ - Kevin 2003 Sierra 2500HD LB7
SuperChips Flashpaq 
Straight-piped and resonator plugged When I sit in my truck, does that make it MODded?? Got questions? Help us all out by filling out your signature with your ride's year, make model, and any modifications you've made. | 
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