vortec 454 hesitation/stumble/surge

[454ss]

i have a 1997 gmc 1 ton 4x4 with 454 and 4l80e trans. on light acceleraton, rpm under 2500 or so, it surges and doesnt want to accelerate, sometimes you can hear it slightly backfire out the exhaust when you stomp on it and it doesnt want to go. after 3000 rpm or so it takes off like normal, the service engine soon light hasnt come on at all. the egr valve has been replaced, the fuel filter has been replaced, the fuel pressure has been checked and ok, the fuel pump has been replaced, the throttle body has been cleaned, the iac has been cleaned, the mass air flow sensor has been cleaned,plugs wires cap and rotor have been replaced, coil has been replaced, has been checked for vaccume leaks and seems ok, pcv has been replaced, upper and lower intake gaskets have been replaced, the o ring seals on the injectors have been replaced, i dont know what else to do. i have had it to 3 shops and nobody can figure it out, any ideas? thanks for any input.

[422 SS]

Take it to a dealer.They can tell you exactly whats wrong for 50-60 bucks whenever I have a mystery problem it goes to the dealer for troubleshooting.After they tell you what's wrong you can buy the parts and fix it yourself.

[99-2door]

My brother's 96 454 was doing that and it was the MAP sensor.