I have had the case of the miracle tank happen like you said. 200 miles on a half a tank. 30 miles later and it was at 1/4 tank. It has a strange way of working itself out.
I thought I was getting some phenominal gas mileage the other day with my Ranger 4.0 (not a good engine for gas mileage) when I still had a half tank after going 225 miles. The next night, I walked out to my truck and my f-i-l was putting gas in my wifes car from a 5 gallon can of gas. Turns out that he put 5 gallons in my truck 2 nights before. So much for my great gas mileage!
