I've had my '17 Eco for about 2 weeks now with about 650 miles on it. I've been doing a lot of running around town with it, taking it for joy rides, etc just to get miles on it so I can tow freely. I did tow the Ranger Friday night about 40 minutes each way. The truck drove almost like it was empty. The amount of power this truck has is incredible. I am hoping to get the miles up close to a grand before July 3 when I'll be loading up with my family and our stuff for a 6 day trip towing the boat 3 hours each way.
As for the start/stop, I don't understand why everyone gets so bent about it. It was weird at first, but I don't mind it at all. It can be disabled each time you get in, or permanently by having the dealership turn it off or getting a program called FORSCAN on a laptop and buying a $80 connector to plug into the truck. There are insane amounts of mod's you can do thru FORSCAN, most of which I am not interested in (I do not have it). In 2017, only the Eco's (both 2.7 and 3.5) have it. In 2018, the 5.0 gets it too. You can't just plug the trailer light connector into it because the truck knows it has a plug in and changes other things, not just the start/stop (can't remember exactly what).
The 10 speed is insanely smooth. It's hard to tell it's shifting. You hear it more than you feel it.
My mileage so far is 16.4 average since new. That's a lot of short trips around town and driving to work. The 40 minutes towing the boat is the longest I've taken so far and averaged 14.6 on that trip running between 65 & 75 on the highway for 90% of that drive.