Please help me identify 5th wheel towing issue.

I too tow with the Andersen and MorRyde, and it's a pretty smooth ride, some road conditions will create some chucking. Having the ability to adjust my aftermarket air bags , there has been on occasion where I could adjust the air pressure and it smoothed it up. But that has been rare . Generally it’s just the expansion joints .

Hopefully you will get it figured out , your description of it sounds somewhat unusual .