[spacemanspif]

I'd be interested to see what could come from on a tune on these engines. My Monte Carlo has a 2004 5.3 that came with a mech. fan but was removed for an electric unit for better packaging. I'm getting 19mpg driving 70mph with 28" tall tires and 3.73 rear. I have somewhat of a tune from the company that deleted VATS, rear O2s and a few wires but I think it left room on the table for better power and MPG. If you have an extra $700.00 that you don't want, HPTuners is software for home tuning just like your son used on his Subie. Many on LS1tech swear by NGK TR55 spark plugs, at $2ish/piece they might be worth using. Stock are iridium, I think, and good for 100K miles. There is a big debate all over the internet about what is ACTUALLY better; copper, platinum or iridium. Many say copper is best but needs more frequent replacing whereas iridium holds up longest but isn't as good. I still don't know, but like copper plugs anyway and think that $20 in plugs once a year isn't a bad deal.