Having spent tons of time installing mods to all sorts of cars in a shop, I have to make one note about the Diesel statements made above me by someone. While you are keeping your EGT's low while pulling, you are not getting that 10-15% better gas milage because you are dumping as much fuel into your engine as the injectors and fuel pump will allow.
Any car that is spewing black smoke out the back, whether its a 3 cyl gas or a huge turbo diesel, is not getting optimum gas milage while spewing black smoke. It is in fact over boosting and running rich to lower EGT's (in a gas engine). Or in the case of a diesel, it is leaning the mixture to stop afterburning which will raise your egt's. Bottom line is that you cant get "more power" while "increasing gas milage". i can switch tuning maps all day long on my WRX if I want, but you can't get both at the same time. Aftermarket engine tuners are kind of a snake oil in this way.
Will your power output be higher? Yup. But is it healthy for the engine over time to run in a way it wasn't designed? Not so much. I am all for modding a vehicle, but understand that modification for using a vehicle for it;s unintended purpose will shorten the life of the vehicle. A stock Cummins in a Dodge should not be used to tow a semi trailer often, even if it can. Get the right tool from the job and it will last.
(Or mod the f out of it to go really really fast)