I have a 2006 Silverado 1500 Flex fuel that is up to 230,000 miles. It still runes pretty well except for some lifter clatter on startup. I also have a 1999 that is my parts pickup. My question is, are there any differences in the 1999 vs 2006 block or heads that would prevent me from doing a full rebuild on the 99 and dropping it into my 2006?

 

I assume you have the 5.3L engine on the 2006. The 97 to 2007 is the Gen III and the block should not have changed. When building the older block the flex fuel design would have to be considered in when rebuilding, might be easier to buy a complete engine and trade swap the older block