I read through the initial post and see the OP inspected his stabilizer bar bushings.
There are many products available that address handling. I lean most toward replacing the under-rated stock stabilizer bars versus adding rear air bags. But that is surely a personal decision.
Our old 1983/84 Toyota chassis motorhome
HERE that we had for many years, had very serious handling problems. Heavy duty stabilizer bars were not available so the other practical option was to add rear air bags. They did the job well for vehicle control, but in order to be effective, they required a good amount of air which increased the harshness of the ride. I feel heavy duty stabilizer bars achieve the same without making for a more rough ride.
