Take the rig to a CAT scale. Weigh with and without the trailer attached. The brochure empty weights mean nothing.
I'm betting the trailer weighs in at 9000-9500lb. Meaning the hitch weight should be around 1100-1300lb. Add in passengers, bolt on items and gear in the bed and you are either:
- Over your payload which can result in a squishy suspension and tires that can cause issues.
- The hitch weight is too little which can cause sway (10% is bare minimum and much better to be 12-15%)
As others have said, this is really 3/4 ton truck territory. No way I would consider anything close to a 12,000lb trailer behind any 1/2 ton.