I have a fleet of 4500 Ambulances. Two of them will die randomly on the highway, usually after being ran for an hour or more. We tow them home, because they will not restart. After the fuel system is worked on, new filter, prime it, release air, etc, it starts and runs great. A day later, same problem. Our GM shop is baffled. The have replaced the pump, filter, fuel caps, etc. The mystery problem continues.

Anyone out there have any ideas???? Please??