The Reese dual cam system is picky about the detents on the WD bars centered over the CAM lobes when driving straight. You can appear to have everything else adjusted correctly, but sway control design of those cams can fight each other.
My TT tows great behind my friend's dually without WD. Both my prior F-150 and current Suburban need WDH for the TW and I have the Reese Strait Line with 1200 pound bars. When the system is adjusted poorly, 60mph is uncomfortable. When it is adjusted correctly, 75mpg is rock solid.