On your fuel mileage, IIRC, the KC area has alot of 70 miles per hour highways around it. On top of this, temps are headed generally downward on our march towards winter. The best things to do, to get that mileage up, is to first, drive closer to 55-60 miles per hour on the highways, leave the A/C off, and learn to look well ahead to utilize every possible opportunity to coast. I'll also ease onto the brakes as I get to 40 miles per hour, just enough to get the engine to cut off to EV mode when I'm slowing. If you have the hybrid computer, the more you can keep that green bar pegged from coasting, the more you'll see those MPG's climb. My very first tank of gas came out to 35.6 mpg, according to the computer.

Also, is the Mariner hybrid AWD ? This will cost you a few mpg.