kaydeejay,
You being an auto engineer etc and a 5th wheel owner, I'm surprised you mentioned the 2500 HD brakes being "tested". The truck brakes do not stop the 5th wheel, the brakes on the 5th wheel stop it. We'd pulled our 36" 3 axle Carriage with a gvwr of 18,000 lbs and a pin weight of 2730 lbs several times with our 2004.5 Chevy D/A CC LB 4X4 truck with having the 106 gal aux tank in the bed full of diesel fuel. Never did the truck have to stop the Carriage. When you apply the brakes, the Carriage brakes would actually pull backwards on the truck and also help to stop the truck itself. That is how it's supposed to be because you sure don't ever want the trailer trying push or pass the tow vehicle. That would be a very good battering ram and a sure disaster on rain slicked road or hard stop!
When not pulling our 36' very heavy Carriage 5th wheel, the truck was pulling our 29' Carrilite that truck scale weighs 12,840 loaded ready to go or our 11'4" Lance TC as that's all the ordered new has ever been used for during the last just over 150,000 miles since new. BTW, still has the original rear brakes and not needing replacing yet and the front pads were replaced at just under 125,000 and still had approx 30% left. Replaced them before hauled the Carrilite to Florida from Michigan as I sure didn't want to have to do it down there.
The truck has 5000 lb airbags, Rancho 9000xl adjustable shocks, and 265/75/16 "E" Michelins at 3415 cap ea rather than the 245/75/16 "E" with 3042 ca ea OEM tires. Handles all our loads carried excellent and drives and rides great and no DPF or DEF and that's why we keep it and probably for another 150,000 or more miles as it's never had or needed any repairs other than scheduled maintenance. We only tow at 58-60 mph as I know we have a lot of weight and like arriving safe.