The reasons I ask about a “tune” in the truck is because that became the source of my chucking in a long box 2016 Ram.
I came to the conclusion it was the truck because no matter which of my 3 fifth wheel trailers(cargo and flat deck and Cedar Creek) I towed it would chuck.
One should not assume it’s a hitch or trailer weight.
My tune was an EFI live tune. With the first version...no chucking. With the 2nd alternative one immediately I noticed the chucking. When the installer re-installed the tune with slight changes in the mapping...smooth sailing.
Hook your trailer onto some other trailers to confirm it’s not a truck issue.
I would also suggest you look at my post about trailer shocks.
If you have them the way they are mounted may make them useless and in fact be causing a ride issue with the trailer.