The 2001-2004.5 model year Duramax is an LB7, and the vehicle will have a number 1 (one) as the eighth digit of the VIN.
The 2004.5- 2006.5 model year Duramax is an LLY, and the vehicle will have a number 2 (number two) as the eighth digit of the VIN.
The 2006.5-2007 model year Duramax is an LBZ, and the vehicle will have a letter D as the eighth digit of the VIN.
The 2007.5 model year Duramax is an LMM, and the vehicle will have a number 6 (six) as the eighth digit of the VIN.