I'll agree with Nate.
Also, some years ago I drove through Wyoming, where the speed limit is
75. Unfortunately, there was a massive headwind, and the best I could
do by myself was about 47mph, getting about 17mpg instead of the usual
30. This was 4th gear, almost full throttle. If I put it in 5th gear
I would just slow down.
When I was lucky, I could catch the back of a tractor trailer and
draft along at about 60. But sometimes, a gust of wind would hit the
trailer from the side, and it would swing out into the next lane
over. This exposed the front of my truck to the headwind, and it was
just like slamming on the brakes. It only took about half a second
before I was out of the draft (never to return), and I'd have to
meander along at 47mph and wait, sometimes an hour, for another
tractor trailer to come by.