I HAVE A 1996 JIMMY THAT HESITATES AT START UP?

I HAVE INSTALLED NEW PLUGS,PLUG WIRES,CAP,ROTOR,PLUG WIRES,TEMP SENSOR,BOTH OXYGEN SENSORS,M AIR FLOW SENSOR,NEW FUEL PUMP,NEW FUEL FILTER,NEW AIR FILTER,DOES NOT ALWAYS ACT UP,NO RYME OR REASON TO WHEN IT ACTS UP.USEALLY IT ACTS UP FOR THE FIRST 5 OR 10 MINUTES, IF I GIVE IT FULL GAS FOR APROX 10 -20 SECONDS IT WILL QUIT,VERY SELDOM DOES IT EVER HAPPEN WHEN ENGINE IS WARM