Payload and rear axle ratings are your limits for 3/4 ton diesels and 5th wheel RVs. I have seen many 3/4 ton diesel tire and loading stickers with 2200-2400 pounds of payload, with some in the under 2000 pounds.
Payload should include the weight of people in the cab, things to occupy their time while traveling, cargo in the truck bed, 5th wheel receiver (150-250 pounds) and pin weight typically 20-25% of loaded RV weight.
10k-ish dry means 11-12k loaded with likely over 2000 pounds of pin weight. Plus 200 pound receiver leaves little capacity left for any people in the cab. and that's why you see so many 3/4 tons squatting. They are overloaded despite being 5k under tow ratings and GCWR.
Find a 350 single rear wheel for the extra 1200 pounds of payload.