All the claimed gains are "up to". meaning that if you have an extremely modded engine you can see those results. Engine chips normally net about 3-5 hp and 1-2(maybe) MpG. A factory engine wont see alot of gains, definitely wont see any seat of the pants hp. The best thing to do is complete whatever mods your gonna complete then get a flashtuner such as SCT xcal 3 or 4. This way your tune can be changed as your mods change, its selectable, you can store the factory tune , and reset the device for the next vehicle if you choose to trade up. Your best mods are gonna be pulleys, intake exhaust, gears, and if you really wanna dig in a sweet port polish job on the heads and matching ports.