I too have the same problem with my 2015 Expedition. I have tried everything. I've purchased a new WD hitch which helped a little but didn't cure it. The trailer doesn't wag like a dogs tale, the two units together bob and sway in the lanes of the highway. I do use cruise control and it has bobbed and weaved enough to set off the anti sway system on the truck and auto apply the brakes and shut the cruise off. I've also been told that my factory tires (2 ply) might be spongy and that the new Expeditions now have independent rear suspension that might make a difference. I've raised and lowered my chains on the WD hitch, I've ran out of things to try and I'm not going to keep throwing large sums of money at the problem.
