FWIW... You said " a 2008 Keystone Laredo 5th Wheel with a 7740 Dry Weight and a 1440 Hitch Weight according to the manufacturers labels. It's a 30 footer with one slide".
Brochure on the 2008 Laredo 265RL 30' with one slide is 7645 dry with 1455 dry pin. Pretty close to your 7740/1440 numbers. It also has a 1/2 Towable sticker on the side by the door.
Fully loaded for a short camping trip stopped by the CAT scales. Camper was 9840 (or about 1200 # of stuff). Pin weight was 1660.
So it wasn't 20% of GVWR but most likely over the truck's GVWR