Let me see if I got this straight.

LY5 - 5.3L engine with AFM, found in both the 2WD and 4WD Silverados.
LMG -Flex-fuel version of the LY5 used in the 2WD only versions of the Silverado.
LC9 - Flex-fuel version of the GM's LH6 engine, received a 15HP increase, and is found in the 4WD Silverados only that are flex fuel.

Is this correct?