Two thumbs up for mid-40's mpg @ 77 mph! My Rio's mileage drops like a rock as I speed up. Most of my semi-rural driving is @ 50 mph unless someone is close behind me and the speed limit is 55.
Congrats for keeping the wife happy on a 400 mile road trip. My wife refuses to even discuss going to Dallas {>700 miles one way for me} in the Spring in my Rio. We'll be sucking gas in our Silverado pickup.
The bright side is it's a comfortable vehicle and rides great. It's also cheaper than renting a fuel efficient car that she would agree to do a road trip in.