Hi, you said that you are using the factory gauge? If so, what part number sending unit do you have installed? I will tell you from experience that the ones that are sold at most parts stores are the wrong OHM's! This is because of an interchange discrepency that happened years ago and was never fixed! The most common sensor sold for our A-bodies today is a Standard brand "TS17". This is the incorrect sensor! The correct sensor part number is "TS205"! I was in parts for 19 years and found this error by specing out the sensors in an old Blue Streak catalog. Hope this helps! Lee.