Just for more "info" on my personal towing experience, I'm old, so I have "been there and done that" experience to look back on with this subject..
Towing with the Ecoboost was yet another new experience I had to learn however.. So, since 2014, I have been learning how this truck likes to tow!

I think I have it "dialed in" now, but there is always room to "learn more".
Like was said already, you need to use the 6 gears to keep the engine in it's "happy" power band.. Not it's "Eco" mode...
Low rpms when you need power, is the recipe for an overheated engine. Bottom line... These Eco's like it in the mid to upper 2-3,000 rpm range. I like mine in the 2200 rpm range when just cruising down on a flat hwy going about 65 mph.
For my truck, this is in 5th gear. I lock out 6th for the most part unless I'm going down hill and my speed can be kept around the 65 mph mark without having to ride the brakes or even touch them..
I only use the "tow/haul" button when cruising on the flats. This is because when you hit the brakes, the trans wants to downshift. This helps a lot when you need to slow down in a hurry, or just for the up coming stop light while towing..
You also don't want to ride the brakes when going down hill... This is probably the most critical part of towing.. You over heat the brakes, there ain't no more options if you are still bombing down the road, or that slow moving car is in front of you!
This is when I turn OFF the T/H mode and then use my +- button to control my down hill speed. I try to keep the rpms in the low 3000 range and just TAP the brakes as needed... It's a game you have to learn how to play, just like poker...
If my rpms are too high, I'll hit the brakes hard to slow down quickly (make sure no one is ridding your a$$ at the time!) Then let off and let the speed gradually go up again. The longer you keep off the brakes, they have time to cool down and when you are going too fast again, repeat. If you just ride them to hold a specific speed, you will boil them in a couple of minutes and then you have zero brakes!
Anyway, I've rambled on for way too long.. If you want more info, PM me and I can give more of my "experience" doing this thing..
Mitch