what I did was install an UltraGauge. as long as you are correctly entering the gas you put in, I have found it to be extremely accurate to less than 1/2 gallon. Keep in mind it is not sensing the fuel in the tank, it is computing burned fuel based on all the sensor readings.
YOU NEED TO HAVE THE CIRCUIT TESTED TO DETERMINE IF ITS A WIRING PROBLEM A SENSOR PROBLEM OR JUST A CORRISION PROBLEM. I CAN'T ADVISE YOU ANY MORE TILL YOU HAVE THAT INFO.BY THEN YOU SHOULD HAVE AN EST FROM THE AUTO REPAIR SHOP. SOUNDS LIKE THE GUY JUST GOT A CODE AND REPLACED THE PART. THATS THE PROBLEM HE NEEDED TO TEST THE CIRCUIT AND FIND THE REAL PROBLEM. SORRY