I don't know how relevent this is with a Chevy, but when doing research on getting my father in laws '52 Dodge 1/2 ton running, I came across an intresting tidbit regarding warm fuel.

The placement of the fuel pump in the Dodge 230 is just below the exhaust manifold, and requires a heat sheild to protect the line going from the pump to the carb.. I guess when that line gets too hot, the fuel quits flowing.

If it still won't run with the gas cap off, and you've already replaced the condenser and eliminated other electrical potentials, the fuel line running to close to heat sources might be something to check.

an idea is only stupid if you think about it rationally.