What is causing my engine to ride rough while attempting to maintaining speed? on 1995 Buick Park Avenue

I recently replaced my upper manifold & gaskets, plugs & wires, pcv valve, thermostat, fuel injection o-rings, throttle position sensor, coolant temp sensor, fuel pressure regulator, and changed my oil/filter. I also have 112K on the engine.

Asked by for the 1995 Buick Park Avenue