I have a 2007 Pilgrim 39' 5th wheel (So there is no manufacturer to refer to nor any warranty to worry about) that comes in at 14.5K GVWR. I normally leave this camper at my site which is about 250 m...
Issues with nose high towing: *Chucking due to pin weight getting lightened *Sway due to light pin weight *higher weight transferred to trailer rear axle/tires...even with equa-flex
2007 vintage.....I would be checking the springs. Still have a good arch or are they flattening I would address the springs vs nose high condition unless one of the above items is occurring