That is interesting. I've felt like sometimes the weight distribution makes the steering act kinda funny sometimes -- I've noticed the steering wheel angle being different from time to time in all of my 1/2 ton TVs. But not a consistent angle driving down the road. I haven't noticed anything similar w/ my F150, and I have sway control and factory trailer brake controller as well.
You can turn off the sway control. I'd try that first.
Note -- once you get everything squared away, you're gonna love towing with the Ecoboost!
