02 Tahoe, Excuse my newbie know how, I have not owned a domestic in some years. My question is I thought the LS series engines 5.3L were cast block with cast iron heads? Mine has aluminum heads so I thought that was odd. Or am I just confused? EDIT: Never mind after some digging around I see that the Z in the 8th digit equals an L59 Flex Fuel engine. Need to look up an odd rattle, sounds like the broken bolt issue on the flex plate.