I'm familiar with programmers, but what is actually involved in a custom tune? I really know nothing about it. What hardware do you get when you order a custom tune? What kind of performance gains can you expect assuming you have the basic bolt-ons already installed? What happens if you want to go back to stock for some reason? What happens if the computer is reset for some reason, can you reinstall the custom tune? Will it increase or decrease the gas mileage, assuming you keep the same driving habits?