[mpg_numbers_guy]

25 MPG is really good for such a large vehicle.

I wonder if the engine is actually "running" (i.e., consuming gas) or in some sort of DFCO mode like traditional gasoline cars have, where if the RPMs are above a certain number and your foot is off the gas, it cuts off fuel to the injectors while still leaving the engine "on". In that case the resistance of the engine spinning would add some sort of charge to your hybrid battery without actually consuming any gas.