As suggested.....
Look on drivers door jam for TIRE AND LOADING INFORMATION sticker (YELLOW)
It will list "The combined weight of all passengers and cargo shall not exceed XXXX lbs)
That will be the specific payload for Your truck.
Add your weight above 150# , all passengers weight, all stuff inside cab and all stuff in bed of truck-------subtract that total weight from your payload number and that is how much you can add to your truck in the form of pin weight.
In reality.......
A 5th wheel that has a gvwr of 14K is what your truck should be able to safely tow
YOUR 2016 250 is rated similar to my old 2007 3500
I tow a 14K (13,873# scaled weight) 5th wheel
I am OVER truck GVWR
Not over on RAWR or Rear Tire Max Load Ratings (you have more tire capacity then I do)
Nor am I over the GCVWR
I use axle ratings, tire ratings and Gross Combined ratings vs just GVWR
Stay within THOSE ratings and you are good