My Diesel Truck Gets Bad Fuel Mileage After Dealer Reprograms It

2000 Ford F150 Stalls while driving. 2000 Ford F150 Stalls while driving plugged converters? 2004 Nissan Frontier Idles fast. 2014 Nissan low oil pressure light is on. 2020 Duramax Truck gets less mileage after the dealer reprogramed it. Does a car get better mileage when tank is full? 1986 Camaro Carburetor wants LS conversion or fuel injection. Buying and driving a Ford Maverick.