Fuel Tank

1997 OLDSMOBILE BRAVADA, I filled gas tank and took a one hour ride back and forth. Went to start my truck and would not start. It seemed like it was out of gas. But I new I had just filled it the night before. So I questioned the fuel pump. I went to drain the tank and I realized the tank seemed like it was empty. So I put a gallon of gas in and the car started. I went to the gas station thinking the truck was emty but It only took eight gallons of gas meaning there was still atleast a half a tank of gas. Knowing it is a eighteen gallon tank,I am confused as to why this truck would not start with a half a tank still in the tank. If anyone can help, please let me know.
thanks,

The fuel pressure needs to be checked next time this occurs to get any ideas.