Is this what you had in mind? Or close to it?
Easy to build with some 1 7/8" schedule 40 or even 11ga 2x2 or so. Very handy setup. Move base of a frame farther up into truck, use chains to hold A-frame and to adjust the position of A frame. Winch it up until it hits top. Keep winching, A frame comes up. Chain A frame up in position, and lower winch to lower your Elk.
There is another method that uses the front winch that I have used in Africa in Land Cruisers on many occasions. It's not a great idea for a 5 ton for many reasons, but definitely can be done. In fact, I'm designing it now. Can't find a picture. I'll just have to see if I can build it.
I did build one for my Kawasaki Mule. It was able to pull deer Aoudad and even Red Stag into the bed using the front winch routed over the top with a series of pulleys. It works! But, for a 5-ton, it needs a lot of designing. But it can be done!