I doubt you're having vapor lock problems. All I own and drive are antique vehicles and I have never had one suffer from vapor lock. I've had problems that I thought might be vapor lock but further investigation and testing proved otherwise.
New aftermarket fuel pumps are absolute junk straight out of the box, all made in China regardless of brand name. Send your original pump to Then & Now Automotive to have it rebuilt.
I had two new ones fail in quick succession as did another member of this forum.
Another common part with the same reputation is the condenser. All are junk, all are from China. One failed on me after less that 1500 miles. Go to the electrical section of this forum (pinned at the top) and read the article by Jon G who makes 200,000 hr condensers for our trucks. I put them in everything I own.
You first need to test the fuel pressure of your pump and test its output. When it dies, is fuel actually making it to the carburetor? Disconnect the line at the inlet and cranks the starter to find out.
When the truck dies, look down the throat of the carburetor and manually goose the throttle. You should see good solid squirts of fuel from the accelerator pump.
Also after the truck dies, test to see if you have spark at the distributor cable on the top of the dizzy. You may have a coil that's breaking down in the heat.
If you're sure its a fuel problem after testing everything, consider replacing the Rochester with a Carter.
