Like others have said, To take the guess work out just load up the truck with everything and everyone that will go with you on a trip. Make sure you have a full tank of fuel and go to a local Cat scale at any near by truck stop. Get the weight of your truck and subtract that from the vehicles GVWR. Whatever you have left is for the trailers tongue weight. From what I have read over the years you should always figure your tongue weight to be 12% of the trailers GVWR. Also don't forget to factor in the weight of the WDHitch itself(about 100lbs).. Best of luck!
Kevin