2001 Crew cab F-150 4x4 with a 5.4.
Drove the truck to the gas station after work filled the truck up and then it would not start. let it sit for about and hr and it started right up.
Another time
Drove the truck less than 15 miles, cut it off for about 30 minutes and some times it will not start. It will turn over but will not start. Let it sit for an hour it would start.

 

Check fuse seating and PCM relay by swapping with another in the box.
Check seating of the crank position sensor behind the A/C compressor.
With nothing to go on there are the places to start.
Good luck.