I have a 2000 ford f-150 with a triton v-8 the truck runs fine but when i drive it a while and then shut it down and try to start it a few minuets later sometimes all the engine does is spin over real fast, wait about 5 min or so and it starts right up and runs fine again. i have changed the fuel pump relay and fuel filter with no results, also no check engine light comes on. could it be vapor locking?