Engine problems when hot, please help

[1970heavychevy]

Any help greatly appreciated. I have a 70' C10 with a 70' 350 Impala motor. Motor was rebuilt 5 years ago when it belonged to my dad. He drove it 2 years before giving him the same problem. I bought it 2 years ago knowing it had a problem. It fires up no problems and seems to idle fine. When it gets hot, after idling for 10 minutes or a short drive, it loses 85% of its power. This is a run down of what I've done in the past week but no luck.

My dad had the fuel tank sock replaced when he had it.
I replaced all the fuel lines, fuel pump, fuel filter, added a regulator, and cleaned the carb (Edelbrock 1405).
Replaced the distributor cap, button, module, coil, and plug wires.(HEI)

What else could it be? I want to get started on the fun stuff of this build but won't until its running.