Is that how you maintain 55MPG? I think that is just crazy. Is your road pretty flat? I'm lucky to average 44mpg over a tank, sometimes 45.Weather seems to have a lot to do with my fuel economy. Heat and wind can really impact mpg.
I regularly run I-10 between Arizona and California. From about May to October the prevailing winds out of the West can cost me 3-4 mpg heading into CA. On the return trip to AZ if I catch a tailwind it can cancel out most of that loss but not always all.
Then there are those trips where I fight headwinds both ways. Depending on time of day the winds can switch from West to East.
Add to that it’s HOT (less-dense air = decreased efficiency). The turbo helps to negate this impact but it’s still noticeable.
Winter to Spring the winds die off for the most part. It’s on those calm, cool days where the car is most efficient.