I see all you guys talking about LLY or LMM how can I tell which one I have?

The 2006 & early 2007's would have the LLY. The 07i or 2007.5 and 08 models would have the LMM.

You can check here for additional information. Build your vehicle and there is a ton of technical data in the On Line Order Guide.

http://eogld.ecomm.gm.com/dmdindex.htm

Check under your drivers side sun visor. There is a sticker with a bunch of numbers and letters, one of the rows has the letters LLY or LMM....thats you motor version and the build codes for whatever else came with the truck.