it sounds like maybe you have been calibrated to a closer correctness. i received my scan gauge after i filled up (friday) so i had to re-fill up and hit done on the gauge, effectively zeroing it out. considering our cars are pretty similar, i see the numbers you are saying you got before now. without the scangauge i measured best of 42 highway, so the numbers i see on there are in the 50s sometimes holding on highway, but i feel like that will go down once calibrated.
everything i read on it says the averages and the instant mpg will become more realistic as you use it. also, keep track using your odometer, that way you can tell if you're still on track.
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