1991 Chevy Camaro wont rev up?

Engine Mechanical problem
1991 Chevy Camaro 6 cyl Two Wheel Drive Automatic

my car is just recently idling again. Before it was starting up and dying. I have replaced the battery, altenator, fuel pump, ignition module, idle air control valve, spark plugs and wires, distributor cap and rotor, and the manifold absolute pressure sensor. When it idlesm I will try to give it some gas but it wont rev up. Ill put it in gear and it will try to move but its like its getting no gas? There is gas in the tank and still noting? What could it be?