I agree with MFL. When towing, I set my cruise control at 62. I may speed up to 65 for brief periods to pass somebody, but when I am by them, it goes back to 62.
The reason I choose 62 is that most people drive on a division in mph of 5. They drive 60 or 65 or 70 or 75. By driving 2 or 3 miles over or under that, I am never in a wolf pack. I am always slowly passing the others, or they are slowly passing me. I never bunch up with them.
I did a test with my previous rig. At 60 mph I got 9 mpg. At 70 mph I got 6 mpg. That is a 16% increase in speed and a 33% decrease in gas mileage. My current rig has somewhat higher mpg numbers, but tested out to that same ratio.
