Rob, I just purchased a ProPride for our 2016 Jayco 28BHBE, being towed by our 2006 GMC Sierra 1500HD. I towed our trailer home about 200 miles yesterday for the first time, and I experienced the same thing you mentioned; a little "sway" at times from the trailer within the 65-70mph range. I even felt it at times when a car would pass me. It never was close to what I had been experiencing with our prior, inexpensive, hitch setup, but definitely a surprise given the claims of the hitch and other users. It was never uncomfortable to me, but was surprising none the less. And while I definitely agree with a few of the posters here in this thread, that there is no substituted for correct loading and WD, it still surprised me because I have weighed everything and found things to be right where they needed to be.
Sean had told me before I left for our trip to bring the WD jacks up a bit further if we felt any porpoising, which we did for the first 10-15 miles. But now I'm wondering if I just cranked them up a bit too far. We started around 3 inches up, but then went to 4, so it wasn't a major increase. But even that one inch seemed to make a difference.
Anyway, just wanted to let you know I experienced the same thing you did. We aren't going camping again till the end of Sept, but I'll make a few adjustments and post back my experience. I'd be interested any adjustments you make and your experiences as well.