Do you have dual tanks?If the prime is lost on the fuel system, then it is possible that the electric fuel pump (balance/transfer/lift pump) is failing. It is located on the frame rail.
What is the fuel level in the tank? If it is less than 1/4 full, try adding 3-5 gallons of fuel and see if it starts then. If it does, there is an updated fuel level sensor/sender assembly for your vehicle.