Can anyone give me the insight on these programmers for trucks? Are they worth it? Best ones to buy? Your results, and any info would be greatly appreciated, along with any negative affects. I am looking to possibly put one on my 07 F150, maybe get better gas mileage, and just a little more horsepower, to push the 35's that were on it when I bought it. I'm not to positive what they all due. Or would you recommend a "custom tune"?