My dash gas gauge only shows that I have 1/2 tank when I fill it up. The gas light goes on after four gallons of gas used. I know it is a 9 gallon tank?

Hello, either you do not have as much fuel in the tank as you think, or there is a concern with the fuel sending unit or wiring related to this system. A diagnostic tool can e used to monitor fuel level position and even actively command the gauge to ensure it has full range of movement for accuracy. Further testing of the wiring and sending unit may be needed.