I randomly came across the Max Energy Power Programmer Chip by Hypertech months ago. It’s a programmable chip that's used to “hack” your car / truck's on board computer for improved MPG, improved horsepower, to adjust your speedometer due to modifications, etc. I’ve been considering one for my 2001 Chevrolet Tahoe for the those same reasons. From what I can tell you just hook it up to your computer via a USB cable, select what options or "hacks" you want and then attach it to your vehicle using the ODB-II connection and that's it. The chips also allow simple rollback options for returning the settings back to the default manufacturer guidelines.
Every time I’ve needed to have an engine code read it has cost at least $100. So if you have one engine code a year (as you might expect with an older vehicle) the device could pay for itself within a few years. The problem of course is the manufacturer knows this and so the device retails for (my specific model) about $350. I found it here on Amazon.
It’s a shame it’s so expensive. $350 is just too much to take a risk on, especially with only a 30 day money back guarantee.