O.K. it's a 1999 F-150 4.6L 4x4, approx. 65,000 mi. I have had several instances where when hot the truck would not start. It will crank, but will not fire. When you let it cool down it will start. This has happened several times, and recently while at 70 mph it quit as if someone turned off the ignition. When the truck cooled down it started again, but not while hot!!!! I suppose it sounds like an ignition issue but am not sure where to start.... any ideas???