KDY - I suspect you Do Not have a “Vapor Lock” issue, but a boiling the fuel out the carburetor problem. A vapor lock would cause the fuel pump to be unable to supply fuel consistently, since it is not capable of pumping vapor very well. You indicated the AFR was tipping to rich and not towards lean. I think this supports the fuel boiling out the carb and not vapor lock.

Do you have the carb mounted on a phenolic spacer to reduce the heat transfer? If not, you should install one at least a 1/2” thick if you have the hood clearance. Are you running an Edelbrock or Carter type carburetor? If so, they are more prone to the heat boiling the fuel, because the fuel bowls are closer to the heat source, the intake manifold.
Ron