1998 with little power

I could use some help, in November I bought a 1998 ACTY. First two weeks it ran great, then one day while driving and the engine was warm, I lost power and the engine died. Since then, we have replaced: Fuel filter Fuel pump Air vent cut solenoid Solenoid valve Rebuilt carb Spark plugs Head valve gasket seal Ignition Control Module

The truck starts up no problem but may operate at only 20% power or it may run great but most of the time at that 20% power.

We have just cleaned the ignition switch. Still no luck.

Any help? Suggestions? Thoughts?

Thanks so much.