I buy diesel all over the country, pulling loads of various weights and sizes and have never noticed a difference in mileage or power due to fuel alone. You might be surprised at just how much a strong head-wind or a cross-wind can effect your mpg, especially when towing a significant load. I recently hauled a load of equipment from Virginia to California and bought fuel in almost every state in between and my mpg never changed. . . . .just the price per gallon.

This morning I went to a Shell station and asked the cetane rating of their fuel. They called their supplier and were told that this time of year it is 43-46. So, if API score and cetane rating are the same, that is a huge difference. BTW, I ran the tank almost empty and just filled up with BP. They did not know what a cetane rating was but they gave me the phone number for their supplier. I will call them tommorrow.