As for your question of exact overloading...I'm gonna say that the door sticker says gvwr of 10,500. My 4x4 club cab single rear wheel dodge diesel weighs 6500lbs.
You didn't say if yours was 4x4. Assuming 2wd, it probably weighs around the same as my srw truck. If 4x4, estimate for a Dana 60 (1000lbs???). So 7500-ish. Maybe you have weighed the truck??? So (and still assuming weights), you've got 3000lbs for camper, people, food, dogs, all that fun stuff.
Those are your numbers. They don't really work if my estimations are correct, but the truck will handle it fine.