Sometimes we overthink things. Not saying you are. But maybe a little? My truck weighs 9,000lbs on the money with me in it. That's 35" tires, all aftermarket springs and suspension components, warn winch and winch bumper with steel cable, a Ranch-Hand rear bumper, a full set of hand tools/wrenches, all the standard recovery gear (3/8x30' gold link chain, tow strap, snatch block, highlift jack, shovel, axe, tire chains) full size spare, Titan 40 gallon tank in the front position, and standard rear tank. My shell is a fiberglass flat top with a set of home made bars. The interior is more or less stock. I'm a little heavy (the truck- not me....well a little. 6'3" and 250lbs). My 460 powered flatbed truck (identical in nearly every way other than the engine) also weighs 9,000lbs. I've towed 20,000 with these trucks....bunches. They can handle the weight. But- that doesn't make it smart. I'd hate to think I got in a wreck and hurt someone. That sticker on the door is a problem for you. Not for the truck, it's strong. There are, however trucks that are much heavier. Maybe lighten up with an aluminum bed and a light camper. Scrap everything you don't need. It's so easy to pack more than we really will ever use. I do think a dually rear axel will bolt right on. The brakes are different, it tracks wider- I don't think it's really much different than the single rear. It just allows you to bolt on duals without hitting the springs. But you can swap to a dually setup- but that sticker won't change. So looks like to me you need to: truck up, lighten up, or ignore that sticker. Good luck man. I wish you well with it, and look forward to seeing what you decide.