I read this entire thread and also have a lot of experience pulling a similar load. I have achieved similar results. I too have the towing pkg on my 2017 NA 3.5. I have just resigned myself to the fact that these explorers just weren’t meant to pull a load. When I pull a trailer, the first thing I do is push the tow/haul button(according to the manual, this locks out 5&6 gears). Then I don’t exceed 55 mph, I use the cruise, and I stay in the far right lane, and get flipped-off freaquently. This procedure will net me about 12mpg’s. It ain’t pretty, but it gets the job done.