I wanted to tow a Jeep Wrangler Rubicon Unlimited with a Tioga 29 ft. Class C.
I encountered the same problem the OP is having, a 3500 lb. hitch.
I took it to a highly qualified metal worker/welder and had the hitch reinforced and the frame extensions inspected.
He said "You are good to go!"
So we went.
We made several trips across the Continental Divide with that rig. Nothing bent; nothing broke; there were no accidents, incidents, or occurrences; no injuries; and no fatalities.
the Ford 460 in that Tioga did the job quite well.