I've never actually messed with the tuning of one but from the research I did when I was thinking about putting the 5.3 I used to have in my Camaro most people go with the 0411 PCM and use either EFI live or HP tuners for the software. Their flashed through the OBD port so no need for PROM's or a PROM burner like the older OBD1 stuff. As for the harness Painless makes some nice stuff but it can be pricey. Most people get a factory harness and wiring diagram then use the connectors from it to make a custom harness. Those LS engines are sweet and can make some serious power I say put a turbo on the 4.8, as for the 6.0 put a cam and L92/LS3 heads on it. Also keep in mind depending on what you plan to drop them in you might need to change the oil pan and/or intake for it to fit. Also check out Kwiq performance their accessory drive is way more affordable than some of the other stuff out there.