I read over all the OP's posts carefully, and I'm not convinced there is a problem. Its a 3/4 ton truck towing 12k of toy hauler, and all is well on asphalt roads. Its when things get rough, the truck gets rough. Air bags and new shocks could help, but is there really anything else to fix an issue that is pretty normal?
Also be advised, if the TT really weighs 12,000lbs and the TW is accurately weighed and calculated to have 13% TW, that's well over the Hensley max TW of 1400lbs. I have a feeling the real TW is well over 1400lbs, making the ride worse than it needs to be with the Hensley. Shoot for 10-11% TOP TW IMO.
