1
181962
You should watch that more closely and longer. In my experience, if you get it running steady on 2 cylinders you will gradually decelerate. Maybe you had a 50 mph tailwind. If what you say were true people would be reporting 50 mpg, give or take, on a tank of free-flowing highway driving, not 33 or so at the high end.My car's instant MPG gauge is pegged at 50-60 MPG when cruising between 60-70 mph on a flat road. During this time, 2 cylinders are shown to be "off" and I'd assume it's basically FWD at this point.
As for FWD vs. AWD fuel economy, the additional weight in the AWD would be a bigger factor than than the affects of AWD engagement if there is any at all in that factor. Even the added weight of the AWD is small enough that it might not be detectable given the variability of conditions from tank to tank.
I would also not trust the gauge's cumulative mpg reading. I've found some meaningful overstatements in that reading relative to a manual calculation--top off to pump shut off, reset the cumulative gauge. drive, refill at the same pump to shut off, then calculate.