Vapor lock is MUCH more likely to occur at idle rather than speed.
If you are having stalling from fuel starvation at highway speeds, check the fuel tank to make sure nothing is bouncing up and temporarily blocking the fuel pickup.
Jon
Good carburetion is fuelish hot air The most expensive carburetor is the wrong one you attempt to modify. If you truly believe "one size fits all," try walking a mile in your spouse's shoes! The Carburetor Shop
