Hey all this has been bugging me for a while now. I commute daily with my 5.3 9-7 which is 96% highway with generally no braking at all once I get on the highway. What I can't seem to figure out is why the DIC average mgp varies depending on when I got gas. Generally the mpg is the best the day after I fill it up then normalizes as the tank gets used. After this last fill up I got 26.5 the whole way to work the first day and it droped each day until it settles down to 21 which is normal. The previous highest I ever got dic wise was around 22. I go to the same gas station every fill up, use the same grade and do 70 mph the whole highway route. When I first got the truck last November I manually calculated about three tanks which showed a best combined of 17.9mpg since even a little weekend driving and city driving drags the average way down. Of course a sustained 26.5mpg with an awd 5.3 isn't even possible and so there seems to be a few different things going on here. The air filter was new when I got the truck. What do you all think?