My GMC pick-up has a mere 200 lbs rating for the tailgate. I keep an eye on the cables, to see if there are any severed strands. I also have a 'trailer hitch T,' which slides into the OEM trailer hitch, and extends up to the underside of the open tailgate, where it rests against the underside of the tailgate top edge.
The receiver hitch is itself rated at 600 lbs. which is 1/10 of the tow rating of 6,000 lbs for its tow package. I can also extend the steel box-section beyond the end of the open tailgate.
I have an aluminum platform which sticks out another foot+ beyond the open tailgate, and the front of the aluminum platform is against the front of the pickup bed. The steel box-section member in the receiver hitch extends out to a couple inches before the end of the aluminum platform and the vertical adjustable steel box-section ends in a horizontal T, the same one that I use for the open tailgate support, if not using the aluminum platform. I've had the 'Max on it a few times, and I always feel better about carrying it that way, with the aluminum platform being supported on its underside beyond the length of the open tailgate.
However, I've also carried the 'Max using the receiver hitch and the fabricated steel box-section T supporting the open tailgate, and it seems to behave OK to support the weight.