When it comes to posting MPG, we really should all be talking hand calculated MPG & include things like: driving content (speed, % stop & go, terrain, etc), miles on vehicle, load, tire psi, driving style. In fact, the only figures that probably should be considered comparable are those for empty vehicles driven solely on flat freeways at X mph or or those for empty vehicles driven entirely in stop & go driving, and only then when a/c use, tire psi, & miles on vehicle is noted. Driving style for the stop & go driving should also be given. It's probably a safe bet that 2 vehicles getting about equal MPG on flat ground freeway with similar parameters above are also about equally efficient at all other times. My guess is that it is usually the varying percentages of stop & go driving in the figures given that explain their significant differences, followed by average speed, break-in progress, & a/c use. I haven't yet noticed how driving style plays into it but I would think that hard acceleration costs, at least until the TC locks. In any case, stop & go kills our mileage more than the typical vehicle.

A/C costs me at least 1 mpg and possibly more - it's hard to calculate because the times I don't run A/C - I typically run defrost or floor vent and both of those run the A/C compressor also. but the little I have run without the compressor on, the mileage is better.