Must be a drastic misprint or false info.
I totally doubt the rear axle of the 2500HD truck weight actually weighs 11,000 lbs with the empty 5th wheel pin on it. The unloaded rear axle of your GM 2500HD truck weighs approx 3,000 lbs as I have the same GM Diesel Crew Cab Long Bed 4X4 truck and have scale weighed it unloaded more than once. Your 5th wheel couldn't possibly have an 8,000 lb pin weight as NO production made 5th wheel pin weight even goes as high as 5,000 lbs unloaded even in the luxury very high end 42' long 5th wheels. Most are even well below 3500 to 4,000 lbs pin weight.
LOOK at the Rushmore Washington brochure specifications as it clearly lists the pin weight as 2892 lbs empty. Add that 2892 lbs to your 2500HD rear axle unloaded weight and you have roughly 6,000 lbs total before you load any cargo in the RV or persons in the truck of which over 50% of their (persons) weight is on the truck's front axle. Your entire truck's total weight with the 5th wheel attached including 2 adults and a full tank of fuel may weight close to 11,000 lbs on the the total 4 tires.
Your real concern is the max tire capacity of the 2 rear tires at max inflation as that should not be exceeded. Tire capacities and inflations are almost always the weakest link in truck/vehicle loading. Simple to replace the tires with a higher carrying capacity or add airbags etc or an edditional spring leaf. If you have a 4x4 truck, you must have all 4 tires being the same size as in circumference or you'll ruin your transfer case unit prematurely.
Also, best to have all 4 tires be at the same inflation so tire squash is minimized due to the weight they carry maintains the same road surface to centerline point of its axle actual dimension so that each tire revolution of all tires freely moves the truck/vehicle the same distance which doesn't put immense pressure on the transfer case unit which causes heat and premature wear. A squashed tire will travel less distance in one revolution than a non-squashed tire of the same carcas size because the squashed tire has less distance to the road;s surface creating a smaller effective tire circumference. It's the effective circumference that controls the distance made good with each 360 degree tire rotation. Tires fighting each other for distance gained in rotations increases heat, wear, and premature tire failure plus lower MPGs while allowing it.
Doubtful that in real life travel use, you will be at the max GVWR of the 5th wheel and that is something you can control and also the location placement of those items added. Food for thought: 100 lbs added in the rear of an RV averages approx 75 lbs less tongue or pin weight. While 100 lbs added in the front of an RV averages 80-90+ lbs of additional tongue or pin weight. Help yourself! However, do not ever get your tongue or pin weight below the minimum RV unit weight required. 10% to 12% for TT's and 15% to 20% for 5th wheels.
Nearly 4 decades (now retired) of doing vehicle engineering, component design, testing, etc contract or by invite for GM, Ford, and Chrysler Corps with my owned engineering operation. Mostly trucks, vans, and SUVs. Also our 51st year of RVing ourselves. Just want to help RV'ers enjoy and be safe.
A superb CC LB 4X4, GM HD Diesel, airbags, Rancho's, lots more
Lance Legend TC 11' 4", loaded including 3400 PP generator and my deluxe 2' X 7' rear porch
29 ft Carriage Carri-lite 5'er - a specially built gem
A like new '07 Sunline Solaris 26' TT
