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LBZ, LB7, and LLY are the production codes (RPO) for different versions on the duramax. They way that you tell which engine you have on your truck (yours is a LB7) is to look at the 8th digit of the VIN.

1 = LB7 (2001-2004 model year)
2 = LLY (2004.5-2006 IIRC)
D = LBZ (2006-2007)
6 = LMM (2007-present)

The years may not be exactly right, but they should be close as I can't remember exactly which ones were which....the VIN number is the best way to tell.
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