[wagonman76]

A short fillup, and a skewed one at that from a bad pump, is not something you can trust. And gas gauges are usually even less trustworthy. The rain does hurt mileage. But since the tank overfilled, you KNOW you got better than 39. How much better is hard telling right now, your numbers should average out at the next fillup. Also try for longer fillups if you can, that will make less variation in your numbers between tanks.