I have a 2011 F350 king ranch and usually when I fill the truck it will always say it is right around 380 miles till empty. Recently, it only says 250 miles till empty when I fill it. I average around 13-14 mpg city and yesterday I didnt reset it and it dropped down to 10 then to 9.1. But now i reset it and its back right around 14. Is this something to do with the computer or something to do with a sensor ? Thanks for any help.