OK a bit of an update:
I have made some longer highway trips and used 6th gear on them, the miles listed below are all highway miles, here are the results:
Trip 1:80 miles: 17 mpg with AC on whole trip
Trip 2:80 miles: 19 mpg with no AC
Trip 3: 150 miles: 21.45 mpg no AC
Trip 4: 150 miles: 21.35 mpg no AC
I made trips 3 and 4 today, so I was feeling pretty good. I haven't done anything to the car other than using 6th gear on the highway.
BUT:
I made one more trip
Trip 6: 30 miles, ALL CITY MILES, ................8.8 mpg. I wasn't babying it, but I sure as heck wasn't beating on it.
What would cause such great highway mpg, and poor city?