Anybody remember carburetors?

Do you mean it's too rich and floods out at times?

This has been occurring before and after a new engine and

The needle seat, needles, floats, etc in those commonly stick for one thing. Kind of sounds like the float or needle is sticking and flooding out maybe. Do you see gas dribble from the carb, or smell a strong gas odor when this happens?

OR, could it be a non vented gas cap causing a pressure build-up to

I kinda doubt it. Usually in a case like that, the tank collapses, and you starve for fuel, rather than have too much pressure. I'd make sure the cap is correct for the truck, but usually having some pressure is normal. MK

When carb was rebuilt was the float replaced. The floats have been known to become saturated and less buoyant causing flooding at idle or low load.