The problem is I keep getting different information about sway depending where I look or who I ask. My salesman, for example, told us that the difference between a 28 ft and a 33 ft would not make any difference with sway. Can that be right? I
AS you have surly discovered by now their are many reasons a combo can have sway... so no one fix works on all combinations.
Other expy owners who are pulling the same length trailer can have input for you so check with trailer brand forums also.
One of the worst bumper pull sway incidents I've seen when I was on the road was a one ton DRW truck pulling what looked like a 25-28' TT. We could guess till the cows came in why the combo was swaying.
Some ideas expressed here can add to a sway issue so use proper equipment and hit the road for a short run and see how the combo is working. Then make changes.