Hi David and Barbara,
I moved this thread for you (thanks Cheryl).
I have some bad chucking or porpoising (push-pull) when I tow on concrete with cuts (expansion joints) in the roadway that are close together.
Same on asphalt that has repair lines across the roadway. On most US interstates, I am good and on many US highways that are asphalt, I am also good.
I have the TrailAir pinbox, MORyde suspension and the Drawtite (Reese) 15K Pro hitch.
Not sure that one can really eliminate these roadway induced actions. Please keep us informed as to what you learn from TrailAir. From what I have read, they're a great company to work with. If your issue really is the pin box, I trust they'll take care of you on it.
Jim