[wingnut60]

You have a max weight available on the rear axle of the capacity of the two rear tires--that should be around 7500lbs. Any combo of truck weight and pin weight OVER the capacity (also NEAR the capacity) is unsafe. I don't care how much you run over the factory ratings, but you should not overload the tires.
With the rear axle weight you listed, and subtracting 150lbs for removing the cap, you will have about 4000-4100lbs for a pin weight. This does not take into account any firewood, tools, dogs, FAMILY, etc you might carry--all of which will lower the number available for the pin weight.
Joe