1994 Chevy Silverado fuel system or electrical system or ec

This is a 1994 chevy silverado 5.7L V-8. The problem is that the truck will start some times and other times it will not start. Some times it just quits working when you come to a stop or it will keep running util you press the gas. But keep in mind that some times it runs perfect. When it wont start you have to pump the accelerator really hard, this is a TBI (thrittle body injection) you should not need to pump a TBI, when you turn over the engin and it will turn over but not start it has spark. When you finaly get it started black smoke comes out of the exhaust will fuel in it. It runs really crapy too. We have replaced the fuel filter, fuel pump, fuel strainer, ignition coil, ignition control module, distributer cap, rotor, codes.