Got a 99 F150, 4.2ltr V6, that sometimes just won't start. Seems to happen when I've run lots of errands and started it several times. I'd say fuel pump, but let her sit awhile and she'll fire back up and run ok. Been stranded a couple hours twice last summer, then all winter no problems. Today it's up in the 70's, and she's done it again. Intermittant, and seems heat related; but not running hot by the gauge. It reminds me of the old days when a car would vapor lock. Anyone got any ideas? Thanks.