2018 Navigator 6mpg when towing 8k lb camper Ecoboost

I prefer to drive on US and state highways. If people get slowed down for more than 5 miles, I will pull over and let them pass. On the Interstates, there is room to pass. Unless someone has their head someplace it should not be, they should see that they are catching up to me and they can change lanes. That is why there is more than one lane. It is rare in the plains states to have an area where you can't change lanes to pass. The traffic is not heavy out there.