What performance upgrades have you added to increase horsepower and or gas miles

I have found over the years that a 'well maintained' stock engine and it's related systems are hard to beat!! Lot's of promises out there but that is about all you get. IMO!

If you wanted more performance why did you get a 3.7L. in a Hummer? It's still not going to do much better with the gasoline we have available to us, 'Ethenol" decreases fuel mileage. Good luck, I have upgraded exhaust, and it decreases fuel mileage on newer vehicles. Increased horsepower, higher octane fuel, more money for gas! IMO and facts.