1/2 ton towing a 5th wheel

Gvw will not be your worst problem, pin weight will. Take the gvw for the trailer and figure on 23 to 25% as pin weight. Ignore dry weights and published pin weights as they are not real world. Take the number you got and add the weight of a hitch, passengers, equipment you added to the truck and anything else you carry and there is a good chance you will be way over your payload capacity that is on the white and yellow sticker by your door.
Even with a lot of travel trailers a 150 runs out of payload before it runs out of max tow weight. Get more truck or less trailer.