Tink,
Reality bites back.
Same 30 mile stretch as yesterday that gave me 37 mpg: cooler, 15-25 miles per hour headwind, one stop for errand, one traffic light stop and 31 mpg instead of 37.

I plan to check the overall elevation change on the route that gave the 41 mpg reading yesterday. I'm sceptical of the number since even driving with a zeroed Trip B for reference, I did not drive much differently than I usually do. I know that on my daily commute the 300' elevation change is so gradual that it's not obvious I'm hill climbing, but it's enough to make about 2 mpg difference in the trip up vs. the trip back.
Lewis