I got the trip odometer set up and I have driven several tanks of fuel, calculating my mileage the old fashioned way. The trip odometer is also giving me its calculations which seem to be about one mpg higher than my actual mpg.
About 30 mpg actual, driving from 4,500 ft up to 8,800, down to sea level for a couple hundred miles and back. Great mileage dropping from 8,800 to sea level, working the paddle shifters for engine braking.
P.

 

When I was cruising at speed across the desert my actual vs. reported mpg were about the same as yours. The more city driving the higher the discrepancy but never more than two mpg. I'm guessing if I followed all the speed limits on the open road I would get closer to 32