Had been consistently getting 20-22mpg on the highway running empty. Two weeks ago, stopped and filled the tank up. Noticed immediately that my fuel gauge was dropping much faster then normal. Filled up last week and found that driving exactly the same and on the same route I had dropped down to 15. 5mpg. Last night I filled up and got 16. 3mpg. Oh yippy. Asked the attendant at the truck stop that I normally fill up at and he confirmed that two weeks ago they got there first shipment of winter diesel. :-{} So much for a good thing.