No power

I have a 1999 gmc yukon with the 5.7 litre V8 122k on the Odometer. When I hit the gas pedal the truck gets no power and backfires. I've tried the mass airflow sensor, the coil, the distributor, put in new plugs and wires, new air filter, fuel filter, fuel pressure (which is fine), the air intake boot is in excellent condition and there are no codes. Also, the truck does not burn oil or leak it and does not leak antifreeze. What's next? I was hoping to keep this truck for another year or two.