Please help me identify 5th wheel towing issue.

Sounds like you are most likely a bit light on the pin. Weigh the rig and find out what your real pin weight is when loaded for travel. On a 5er you want to be around 20% of the loaded trailer weight. Lighter pin weights tend to have more chucking.

You can get chucking with any rig and it will very according to the road. We have a Demco Glide pinbox and a TrailerSaver TS3 air ride hitch. Most roads we do fine. every once in awhile get get some chucking. I just slow down a bit.

Ken