I havent been following this discussion, but let me add my 1/2cent. We bought a 28 ft winnebago B+ and first trip it was as you decribed. Wallowed and wandered. The rig had air bags but I could not get them to be inglated as I didn't have the right type chuck, tire store could not reach inner tires to inflate! At any rate I finally got the tires inflated to recommended but still wallowed, got air to air bags and it DEFINITELY made a difference. Played with setting and finally got ride of most of it. just need to make a 1 point connector as the air bag fill point is is an awkward place and are individual so kinda hard to equalize. Give the air bags a thought. Mine is an E450 BTW
13000lbs on scale.