If it takes an additional 6 - 8 gallons after the pump clicks off the tank was not full, and the pump shut off early. There is no way the filler pipe, even on an Expedition, could hold 6 - 8 gallons. I have an 86 Blazer that will shut pumps off early, so it must have something to do with the filler neck and vent design that causes some vehicles to shut the pump off early.