I have not read all of the comments above but will make this one.
Reese bars at not manufactured to tolerances that guarantee that the bars are the same length. If you have set up the system correctly and then mark one of the bars for a given side you may see an improvement. I found this after maybe 30 years of using a Reese system. A widow friend who followed we as we would go out weekends said one day that my trailer was all over the road. Then after a couple more trips she said would comment sway not there on one trip and bad bad on another. I checked the setup and found about an 1/8 in. difference in the bars.
This difference is enough to cause the system to become additive to sway rather than subtractive as the bars are actually accelerating the movement at first.
On a nice flat parking lot drive in straight for at least 100 ft. park and check how the bars are setting on the saddles. They should be fully seated on both saddles. Remove the bars and swap them side to side and recheck that how they are seated. If you see any difference that is you problem.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles