Barko1 said everything I would have, except...
Ideally what you need is an F250 longbed
I have a Granby that I had on an F150 4x4 longbed that I added ride rights to, big help, but the truck was still a 150 and the poor 4.6 had to work too hard so now I have a 7.3L 250. I get vastly better mileage and can pass when going uphill.
I know that sounds like a leap but seriously looking at that picture makes me cringe. The weight is so far back and the rear is so over loaded that I wonder how safe it is. GVWR is one thing but what is the weight on just the rear wheels? Looks like the weight of the camper is balanced behind the rear axle. The E tires are essential so good that you have that.
I can't recall where I saw this but on some roads the max weight was limited to 75% of GVWR which I think is a better number to use rather than trying to get to the max.
I may sound like gloom and doom and wonder what others think but the picture says a lot.
You definitely need some kind of suspension upgrade. You have to consider not only the static weight on that rear axle, but also the dynamic loads. Considering how far back that camper sits, I'm guessing the center of gravity is behind the rear axle, hence the camper has a lot of moment, so the forces on the axle and suspension while driving are going to be multiplied because the load isn't centered over the axle.
Think about loosening a tight nut (and no, I don't mean me, which only takes a little whiskey). It can be hard to break a nut loose with a short wrench, but easy with a long wrench. The long wrench adds more moment by multiplying the force applied to the end of the wrench by the distance from the pivot point.