Re: 1st long trip
Constant speed only equals best gas mileage on flat roads. It is my experience that allowing the car to speed up while going down hills and slow down slightly while going up hills produces the best fuel mileage. On my trip that I mentioned a few posts up, I was accelerating slightly down hills and letting the car slow down slightly on the uphills. On that trip I was basically trying to keep the "ECO" light on as much as possible and it definitely seemed to help.
My regular commute (only 15 miles each way) is about half highway and the other half back roads, and I have only been averaging about 14.5mpg on my commute.
Sean in PA
2011 Jeep Grand Cherokee Overland
5.7 Liter Hemi V-8
Adaptive Cruise & Blind Spot Monitoring