i have a 1989 mustang lx, 4cyl. 2.3L. recently the gas gauge has stopped working, like if i sit on an incline it moves to the top like i have a full tank, but USUALLY it sits at 1/2 tank, constantly. Even when it's below 1/2. i have had this car for about 2 years and know my car so i know about how far i can get on $20 in gas, but it would be soo much better if my gauge worked!!! Do you think i need a whole new fuel pump, OR just a fuel tank sending unit? Please help me!!