FWIW, I believe that when we drive we burn fuel to overcome rotational resistance (friction) in the drivetrain, the rolling resistance of the tires, some slight scuffing of the tires against the road surface, and aerodynamic resistance. If we have the air conditioning on, that takes energy (fuel) to make the magic happen.
The rotational resistance in the drivetrain varies as the square of the RPM. So, slower RPM is better. If you consider the pistons rubbing up and down the cylinder, they have farther total distance to go at higher RPM at the same highway speed. So a higher final drive ratio helps reduce the distance the pistons travel rubbing up and down the cylinders.
Aerodynamic drag is a function of the frontal square area of the vehicle, the drag coefficient, the air density, and the square of the air speed. Air speed is the vehicle speed plus any headwind or minus any tailwind. Even a 90 degree crosswind will add to drag.
All else equal, colder air is denser than warmer air. Lower altitude air is denser than higher altitude air. All else equal, 70 mph air drag will be 70 squared / 65 squared = 1.16 times air drag at 65 mph. It will take more fuel per mile to push the Patriot through the air at 70 mph than at 65 mph.
Here are some air drag figures at different air speeds relative to 65 mph with 65 mph being 1.00
50 0.59
55 0.71
60 0.85
65 1.00
70 1.16
75 1.33
80 1.51
Below 60, getting to the highest gear that will get you the lowest RPM per mile traveled and a high enough RPM in that highest gear to get adequate lubrication to the rubbing surfaces should get the best fuel mileage. Adequate RPM to get dynamic lubrication to the bearings used to be considered to be about 1500 RPM. But that probably varies some with the oil pressure developed by a particular engine's oil pump and the size and clearance of the bearings.
As you can see, anything beyond 60 mph you pays your money for how fast you want to go.
For tires, higher air pressure decreases rolling resistance. An interesting thing about tires is that a wider tire adds to the frontal area and air drag. More ground clearance exposes more of the tire's frontal area to the airstream and makes more air drag. That's one reason high speed race cars, even straight line Bonneville salt flat cars, are lowered.
If you look inside the vertical grill slots of a Patriot, there is a plate that blocks the airflow through the top three or four inches of the vertical slots. The bottom line is that close to forty percent of the heights of the vertical slots are for styling and probably degrade the coefficiant of drag for the Patriot. Same thing for the unused fog lamp holes in the lower front fascia of the Patriot Sports.
There has been a discussion on the Subaru Forester forum that removing the cross rails on the roof rack can add close to a mile per gallon at 70 mph. A bike rack with one or more bikes on top of a Patriot is going to add drag. Try putting your arm and hand straight out the window at 70 mph. Then think what that bike on the roof will do. Maybe a rack in a trailer hitch behind the Patriot will save you fuel.
FWIW and IMO and YMMV.
