All tuners decrease mileage. How much it decreases varies but I would bet banks derringer does the best job. More power means using more fuel use which also increases soot production. I would skip the tuner and go pedal monster and idash. That is what is in my truckThanks man, mine is 14.3 over 82k 100% stock. I was just asking because I am really interested in the derringer idash and pedal monster. Just hoping it’s not going to tank the mileage too much.