Thanks for your service Marine Raider1!

If cost is an issue I'd rebuild the 5.3. That saves you a lot of headaches and a million little parts that end up nickel and dimeing you to death. Take the money you were going to put into the new engine with upgraded parts for your 5.3. Or, try and find an LY6 6.0. Same setup as your 5.3 but more displacement and way better heads. (It has the L92/LS3 heads...) The extra ponies are going to be rough on the old trans & rear end though... As soon as you upgrade the engine, lot's of things to consider. I'm not sure if the exhaust on your truck will bolt up to a LY6? Maybe, I just don't know.