Increased pulling power seemed to induce sway...
I would go with a sway control system. I have a single axle trailer. Came up here from Florida. Transmission was slipping. Dropped off the trailer midway and went back to Florida without it. Got the transmission rebuilt. Hitched up the trailer, got 20 miles on the interstate. Suddenly trailer does a wild swaying over 45 MPH. Went to RV place and got a single friction sway controller. Was fine after that.
It was SCARY as hell watching the trailer sway over into the other lane.
It is like having a gun, better to have it and not need it. Blah, blah, blah...