I have heard much about after-market performance chip/module upgrades. There are so many choices. Are they worth it? Which ones are best and require the least amount of modification to install? I don't need a hot-rod, just looking for some reasonably inexpensive means to increase power and/or MPG's without performing major surgery on the truck or screwing up reliability. Other than occasionally pulling a boat, the truck is mostly a daily city driver. Thanks for any input or experiences.