I also do not suspect vapor lock is your cause. Did you ever have a chance to reproduce the problem, and view how much fuel is in the bowl via the sight plug?

Every car is different, and my fuel system is not stock, but I do run a mechanical pump with no return line, and drive my car in the heat without having any problem similar to what you are experiencing. Perhaps I'm just lucky....

I do know how frustrating it is to get the car stuck by the side of the road (I had an electrical ignition issue that put me thru a similar situation for months before I found it). Now that the heat is on in NC, have you ever tried to let the car idle at your house for an extended period, then shut it down for 10-15 minutes, then try a restart? You could load the motor against the converter while in gear to generate additional heat under the hood.