Truck has a good running 360 and the backfiring is the only problem. The only time it will do it is going down a hill trying to hold a constant speed. If I let off the throttle it won't do it, if I accelerate going down a hill it won't do it but if I keep the throttle at one position it will start backfiring like crazy. It just turned 200,000 but other than this it runs great and doesn't burn a drop of oil. Just changed plugs, wires, coil, cap and rotor about 5000 miles ago and it was doing it before everything was changed. Had it hooked to a scanner and no codes came up.