1986 Ford F-150 wont start sometimes once it gets up to operating temp. What could be the problem?

The truck does it off and on, first thing in the morning it start up fine, then after I drive it 10-20 miles or so and shut it off and let it sit for a few mins it wont start back up, will just crank and crank, it has spark and fuel, but if I let it sit for a couple hrs it starts up, will do it for a week or so then all of a sudden stop and start up every time, this is getting really irritating since pretty much all the starting components on the truck have been replaced, what could it be? The engine is the 351 windsor HO with 4bbl holley carb