I'm pretty sure there's an issue in the first equation. A Nm (Newton-meter) is the cross-product between a force and a distance and is a vector quantity (more specifically a bivector), while a watt is a dot product and is a scalar quantity. Converting Nm to W is a dimensional analysis error.

Similarly mileage is force along the direction of travel, but that's moreso a nitpick.

I've actually done the same thing with modeling my car at different speeds! I used linear regression though haha. I have the same car too!What a coincidence. Time to compare homework!

Mileage for gas cars is measured in square meters: https://what-if.xkcd.com/11/

I indeed knew the energy equivalent mileage simplified to tractive effort. What else could it have simplified to?