Chucking - trouble shooting

I’ve come to the point where I’ve concluded there isn’t a silver bullet to resolve the issue

Just part of your questions but your correct ....there is no one thing that works for all chucking issues with a truck and 5th wheel or GN trailer.
I've seen post where the OP had chucking issues. He tried adjusting air pressures on the combo.....new shocks on the combo....even new tires and other low cost fixes that others had done. Nothing helped.
He finally moved the hitch back two inches in front of the trucks rear axle. This cured all his chucking issues. The rv dealer had the pin in his long bed set up 4" in front of the axle.

I had bad chucking issues with 32' 5th wheel rv trailer. It came with a 30" extended pin box which had the overhead about 6" from the end of a long bed DRW. I went with a 12" extended hitch box set to the same height and no more chucking.

What works for you will be just that and may not work for others.

Any wayz ....you could be short changing the trucks load carrying ability and as one member pointed out the overloads maybe carrying just enough weight to have a short compression and a severe rebound.

Google has loads of fixes for those that had the issue. You might wanta' spend some time doing that type of search.