Kinda off topic but I do a lot of mountain driving and so I learned to read the consumption chart as if it's an altitude chart, where higher MPG represents a decline in altitude and vise versa lol. Disclaimer: (Doesn't work if you like to race down mountains)
Excluding downhill glides, I get my best MPG on high altitude plains and plateaus. The air drag there is significantly less than at sea level, saving fuel. On traditional non-hybrids, the reduced engine pumping adds additional MPG improvement, though hybrids reclaim a good portion of this through other means (see "Atkinson-cycle engine') without getting to high altitude. The climb up to those high altitudes does have some MPG cost. The benefit doesn't show up until the road levels out.
