Overloading is a definite issue. I was not over the rear axle weight, but was over the weight rating on the oem Michelin tires, on the driver's rear. The weight was measured with all tanks full (grey, black, fresh, fuel), loaded for a trip with two passengers. At that time I had 7 group 29 house batteries.
I solved it by getting new rims (wheels) and a taller and wider Toyo tire. That gave me more ground clearance and more tire weight capacity.
In the fall of 2019 I wished to replace the broken air bags, and add a leaf to the rear springs. The factory had installed Firestone bags that did not really fit properly. When the local spring shop dissembled they found that there was one broken leaf.
I ended up with timbrins instead of air bags because of the limited space.
Shocks were replaced as well. I'm much happier with the ride and there is yet more clearance.