I bought a 04 Z71 a few years ago and when I got it home, I put it on stands and started crawling around underneath and looking for anything that may seem out of place. Anything wet/damp, loose, shiny wear marks, etc. Pulled front wheels and yanked and pulled and pushed on the suspension parts (ususally worn parts will expose themselves fairly easily). The only thing I would do right now "just because" would be fluids, plugs and wires. That can't ever hurt to know where you stand as far as when it was done. Check the top of the transfer case for fluid leaking. Sometimes these trucks suffer from what is referred to as "pump rub" and it wears a hole in the rear case cover. It's sometimes hard to detect until it's too late. I went ahead and upgraded my pump and replaced the rear cover of mine as a preventative measure, but I didn't do it until I had owned the truck for a bit. I just kept an eye on it beforehand.