vapor lock???????

My son's got an '81 D150 /6 that's started locking up since it got real hot out. Usually "Vapor locks" when it's above 95 degrees outside. Doesn't make it more than 20 minutes of driving. I've got an electric fuel pump, but it still goes chug-chug-chug...stall. At night it runs like a champ. I just wrapped the metal fuel line in rubber hose. (Hoping for a quick fixin the 100 + weather today) But I think we're going to go the route of the new fuel line next. Has anyone used any of the fuel line coolers from summit or like companies?