Try Doin a search, i know Tuning chips have been brought up before.
But there are Upsolute and Powerchips many others too.
I think j Irwan has a Powerchip and he says it gives more power. I emailed Powerchip awhile ago for my C36 and they quoted me 850.00, i wouldent think u would lose MPG more like gain, except for the fact u would problay be flooring it everywhere to feel that extra umph from the chip