When I asked that question I was told the 275/70/18 tires are rated at 3638 lbs per tire at 60 PSI more then enough to cover the 10K GVRW of the 2500.
You should be able to find what is called a load inflation table, which basically tells you how much load the tire can support at various PSI levels. A typical E-rated tire in that size has a max load of 3,640 lbs. at the max 80 psi. Take 3,640 lbs. x 4 tires and that is over 14,000 lbs. which is obviously not needed to support a 10K GVW (loaded weight).
If you assume the front and rear of the truck would weigh the same at the 10k GVW, that means each tire has to support 2,500 lbs. Looking at the load inflation table the tires can support 2,680 lbs. at only 55 psi. At 60 psi the tire is rated for over 3,000 lbs. each, or 12,000 lbs. total, which again is over the GVW rating of the truck.