MISSFIRE AT SLIGHT ACCILERATION

[george w]

I have a 2004 gmc 1500 with a 5.3 and under light acceleration around 1500 and going up a slight incline in high gear it will start to misfiring. If I give it more fuel it will stop misfiring and take off and pull right up the incline. When i start away from a stop and give it lots of fuel it will pull hard. It will not misfire unless its at low rpm. Only on a slight incline or when its in high gear and pulling up a hill around 1500 will it miss fire, i have replaced plugs with new A/C PLUGS, NEW WIRES, CHANGED ALL COILS , CLEANED MASS AIR FLOW AND I HAVE CHECKED FOR VACOUM LEAKS AS WELL. I have run a scan tool on it and the fuel pressure is good, 02's are switching good short and long fuel trim are good, no engine codes at all. When monitoring all 8 cylinder's up a hill and it starts to misfire I can't get It to show a glitch on any cyclinder. It seems to be getting worse.