I have been been towing with my "2013 Ford Expedition EL 4x4 Limited with HD tow pack" for a while and have been very happy with it. The only thing I would change would be a slightly higher payload capacity. In fact that is the only reason I would trade in for a truck.
However...
http://www.ford.com/suvs/expedition/2018
The 2018 Expedition is due for release later this year... 8 speed transmission, 3.5L V6 Ecoboost engine, MAX version available and they are clearly going for the towing market here, no numbers available yet that I can see.
Not to mention they appear to have sorted the crappy headlights out (I changed mine to LEDs years ago), trailer assist is in there as well as the new sync.
Very intrigued to see what the final payload specs are in Max 4x4 Limited configuration...
Just thought I would share...