Just did my first road trip this weekend also. I drove from Jacksonville to Lakeland and back. Before that, 95% of my driving consisted of 20 minute trips to and from work with average FE of 28 - 29 mpg.


On the trip down, I drove at 70 miles per hour and got 37.1 mpg. On the trip back, my wife drove at 75 miles per hour and got 35 mpg.

One thing I noticed is that in the city, both the dash and computer mpg readout are about 1 - 1.5 mpg higher than actual (calculated by trip & gas pump volume). On the highway trip, the dash and computer were closer to each other, but were about 1.5 mpg lower than the manual calculation.

I was also surprised how much 4 -5 miles per hour difference in speed (at 70 miles per hour) resulted in 2 - 3 mpg difference in FE.