I pull a heavy trailer with 4' expanded metal sides and 5' expanded metal ramp.
Every one knows that expanded metal pulls hard thru the wind.
Driving a 2000 F250 7.3L diesel with 4x4 and 6 spd manual trans.
I rarely drive over 65 and get 12.8/9 fairly consistently.
Just the truck with no trailer keeping it under 70, 18.5 is totally doable.
Professionals are people who can do their job when they don't feel like it.
Amateurs are people that can't do their job even when they do feel like it.