[wingnut60]

Gross Vehicle Weight Rating (GVWR) as listed on the door tag LESS the ACTUAL weight of the truck as set up to travel/tow = weight available for the trailer to put on the truck.
Example: 10000 GVWR - 6800 actual travel weight = 3200 left for trailer pin weight.
You can't get this correct figure until you weigh your truck as loaded to go on camping trip--includes all passengers and 'stuff' in truck and bed + fuel and hitch.
Once you have this actual weight (or pretty close number) then you will know how much capacity is available for the trailer.
Also, when you get the truck weighed, be sure to put the front and rear axles on different pads of the scales--front tires on first section, rear tires on second section--this will get you the actual numbers on the separate axles, and particularly the rear axle number.
With the rear axle Weight Rating (RAWR--6100) less the number from your scale weight gives you the actual available weight you can put on the rear axle due to pin weight of the fifth wheel. That RAWR can be pushed some because the actual rear axle weight capacity from the axle mfg is almost always higher then the vehicle mfg puts on it--but you need to look at your tires and find out the max weight capacity for them--X 2 will give you the weight number on the rear axle you should NEVER go over--usually this will be around 7000-7200.
Think this thru--go weigh your truck, loaded if possible, run the numbers and see what is left for trailer pin weight.
As Stripit said, there are many 250/2500 series truck pulling way heavy fifth wheels and not falling by the wayside--up to you how far to push the numbers and how concerned about running near/over the tire capacity you are. Also, as Stripit said, when shopping new/used units--always use the Gross Vehicle Weight Rating (GVWR) as the possibly highest weight and take 20% of that as the expected pin weight.

Lot of numbers to consider, but if you do it often enough, it will make sense.....