Can't stop sway

I have a 15 screw shortbed f150 also. I'm towing a 31' prowler with mine. I had serious sway issues when I first purchased the trailer. Dealer had set my blue ox sway pro up really bad. In my case they had no weight on the rear of the truck. I have one trip so far with no issues after lowering my hitch height and taking links out of my sway bars. I've noticed wind gusts moving the truck and trailer around slightly, but not swaying, more as a whole unit. I find that turning the sway control off in the truck makes me more at ease when towing. Even towing my 16' box trailer I shut it off. I don't like it, maybe it's in my head, but the truck seems much better with it off. I found having the rear of the truck taking some extra weight helped me. I don't have my truck set level when towing, It's slightly lower in the rear. I've also found on a gusty day 5mph will really change how things ride. It took me some tweaking and trial runs to get dialed in. It sounds like it might be in your hitch setup. Best of luck!