I get way better mpg when I take long drives on the highway cruising at 65-70 than I do on periods with mostly city driving. I keep track when I fill up as a ch

I get way better mpg when I take long drives on the highway cruising at 65-70 than I do on periods with mostly city driving. I keep track when I fill up as a check against the car's slightly wonky mpg calculation and it's a difference of 5ish mpg more for highway like the EPA estimates suggest.