I get where you're coming from, but... physics.

When pulling a trailer, even a truck designed to do so has grade restrictions and isn't typically able to haul on a slope higher than a 10% grade (and even that <6 degree slope is considered "extreme"); the principle of the inclined plane says lowering the angle of motion decreases the work* required to lift an object.

Far from "leveling the whole side of a mountain", you're just making roads that are actually traversable under load.

If it's that big a deal, just fill your inventory, jump on a saddled (and tamed) lox, and go wherever you want at full speed.

* by which I mean the scientific definition of "work", measured in joules (ie, one newton per meter, approximately 0.7377 foot-pounds).