1991 GMC C1500 FUEL PROBLEM

5.7L:
I replaced the fuel pressure regulator diaphram, fuel filter and spark plugs. The engine will start fine with check engine light being lit. Once warming up, typically about 3 minutes of running, check engine light goes off, engine starts running rough, black smoke is emitted from the exhaust. I press on the accelerator while in park, engine sputters and jerks then dies. Very hard to start, cranks excessively, if starts runs really rough with black smoke!