I had a similar problem on my 454. Turned out that after a little warmup from a cold start, the fuel in the line would flash to vapor (i.e. vapor lock). If I was driving it at the time it would start to cut out. I actually stood there one time with the hood open and watched it flash over to vapor (clear fuel filter). A combination of things were causing this, including they way I ran my fuel line from the pump to the carb (too close to heat sources), and my failure to bypass some fuel flow to the fuel tank, as was done from the factory on this car. After fixing these things, no more vapor locking. Later I added an insulating spacer under the carb to minimize fuel boil off after shutting the engine down hot. This eliminated excessive cranking after things like stopping for gas or lunch etc.