I will say this about gas mileage, in addition to what others have said about seasonal fuel belnds (which is very accurate), most engines do not see their max/peak mileage until they have about 30k miles on them. Now with regards to “Chips” and “Tuners”, years ago it was the best that most could do to enhance the ignition timing, fuel curve, transmission shift points, etc. It was (and still is) very important that a person verifies that the “Tuner” is ASE certified in both ECM and Transmission programming and IMHO be have current certification by the OEM whose vehicle you want to modify. There are plenty of persons who advertise their programs to be the best and even offer custom tunes, but in all reality, very few actually have credentials in these areas- but that’s not to say that some of these “geniuses” haven’t really caused damage to a few vehicles- just jump over to flatratetech.com and read just some of the comments from the MSE techs!. Perhaps what is equally important is the parameters that can be adjusted are set by the OEM vehicle software…so there is really no “magic” in what they are doing anyway. Now about this new marketing hype that if you have a CAI you need a custom program………….hogwash!!!!!! The OEM software system is designed to adjust the fuel mixture up to 10% (25% on the 2000+ mod engines).......that’s more than enough to handle fuel mixture adjustments up to 7,000 foot elevation change! (for high elevations 8,000+ there are oem software programs for those specific applications) The 5.4 V8 for example if close to stock can only suck in a maximum of 480 cfm and a flat panel filter will flow 500 cfm, there is simply no way any CAI on a relatively stock engine can increase the air flow enough to exceed the ECM’s ability to adjust and maintain the correct fuel mixture. The only reason for the “custom” program to support the CAI is because the design is poor resulting in false readings from the air intake sensors, etc….period! If you look at the dyno charts from many of these supposed HP/TQ increases, they are typically around 5%-7% at peak rpm ranges…….guess what, 5% is a standard deviation even amongst mfg dynos and if you go to this link http://www.fordracingparts.com/downl...ceTechTips.pdf the engineers at Ford racing have a article on just exactly how “tuners” play games with the hp/tq ratings, how calibration can cause misleading dyno results, & some of the “tricks” that are used to gain supposed power increases when in fact, managing your engine….. and the most important item is……these “expert tuners” (at least most) do not have or choose not to test their results (in comparison to the oem intakes) during actual vehicle motion (or simulation- such as a wind tunnel) as the oems do. What many view as an issue (is the plastic intake tube with its noise canceling design) actually increases air pressure. It is the same hydraulic concept used by fire fighters creating water supply where psi is low. By having the air cross the path at a 90 degree angle, the pressure is increased proportionally. Fire fighters use what is called a “4-way valve” or “Blake Valve” at the hydrant where the water is cycled through the fire engine (pump) and sent back into the valve crossing the water flow at a 90 degree angle. In this case it also acts as a sound canceling device! At low speeds, this can reduce the flow a tad (which is what most “feel”), but in terms of peak hp/tq, a good high flow filter is all that is needed. Testand Corporation conducted an ISO standards test on automotive air filters which can be viewed at this link: http://www.dieselbombers.com/chevrol...r-testing.html, and they are a certified test facilitiy.
IMHO, if you live near any major city there are excellent tuning specialists with dynos who for the same price (if not less) will tune your vehicle taking into consideration your specific needs including environmental conditions, for your specific vehicle. IMHO, the best bang for the buck!

If you are comfortable and understand how to tune a vehicle, you can also do this yourself. There are several software programs available, that “Speak Common English” that will allow you to tune your vehicles ECM. One company is HP Tuners, they have a website….they offer two core programs, one for those who are doing dyno tuning and one for the home-garage mechanic (which is priced at about the same as most of the “canned tunes on the market) …this version limits the span of adjustments as a safeguard against doing something outside of the oem scope……basically, keeps you from doing something “too stupid by accident” (grin) and Sniper Delta Force Tuning Software.