Overhead display shows 99.9 miles per gallon every time I start the truck. While driving it settles in around 15 to 20 Mpg. When I accelerate fuel mileage goes up to as much as 22 Mpg, when I am going downhill at 0% throttle mileage decreases to 4-6 MPG.. again increase mileage under hard acceleration decreased mileage when decelerating or going downhill.