When you say "sway when you get over 60" is it a constant sway the progressively gets worse or just random movement? If it's just random movement from wind or passing vehicles, and then settles back to straight, well, that's normal. If it's constant, as in you start to feel a rhythmic side to side movement, that's not normal. As mentioned above get to a CAT scale and check your weights.
I like to do 3 passes through the scale.
1. fully hooked up with WDH
2. hooked up without WDH
3. tow vehicle only
Number 1 will tell you how effective your weight distribution is, number 2 will tell you tongue weight of the trailer, number 3 will tell you unloaded axle weights of your truck.
Take your rear axle weight from #2 and subtract rear axle weight from #3 to get your tongue weight.
Add the tongue weight to trailer axle weight from #2 to get your total trailer weight, then you can do the math to figure out what percentage of total trailer weight is tongue weight. Move load around inside accordingly to get to that 10-12%.
Then adjust your WDH so that your front axle weight in #1 is as close as possible to it in #3.
Takes a little time, and a few trips over the scales, but once you get it dialed it should tow a lot better.