This was actually this past weekend, but took it on an 8-hour trip to northern Alabama for a cousin's high school graduation. Since my wheels and tires aren't balanced so well, they vibrated at 75-85 MPH, my normal cruising speed. I just laid back and set the cruise at 70 for about 98% of the drive and averaged 18MPG. I've never seen my fuel range this high.
First fill-up after drive up and some running around town:
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...And the next fill-up during drive home:
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Since it was easy highway cruising, I went with 89 instead of 93.