A few years ago, I bought a 1994 Dodge Ram 3500 Dually to tow a 32 foot fifth wheel. At the time, I had not found these forums, and was not worried about weight. I pretty much went by the questions I had learned in the late 1950's/early 1960's, which were:
1. Will it move?
2. Will it stop?
If the answer to both questions was yes, we were good to go.
If the answer to either question was NO, fix it, then we were good to go.
Anyway, a couple years later, after several trips over the Rockies, the Cascades, and the Sierras, I decided to weigh the rig, based on the doom and gloom predictions often posted on these forums.
It turned out that the rig was UNDER the GAWR of the truck and trailer; UNDER the GVWR of the truck and trailer; WAY under the registered GVW of the truck; but 3,180 pounds OVER the GCWR of the truck, as shown in the Owners Manual. However, nothing bent; nothing broke; there were no accidents, incidents, or occurrences; nobody had been injured or had died; so I went happily on down the road.
Now, to address your specific question. I towed my Rubicon Unlimited, with suspension lift, body lift, custom bumpers, 30 gallon gas tank, winch, and additional skid plates, behind my old Tioga Class C with 460 V8, with no trouble at all. That includes over the Continental Divide (Marias Pass, Homestake Pass, etc.). Again, nothing bent, nothing broke, nobody was injured or died.
Now I tow the Rubicon behind the motorhome in my sig. Still, no troubles.
IMO, there is a reason the GCWR is not on the data plate, but is only listed in the Owners Manual. It is primarily a "performance number", relating to acceptable acceleration and hill climbing ability. There may also be a limitation involving the hitch capacity, but that can be reinforced or changed (I did have a local welder reinforce the hitch on the Class C).
The bottom line is, it depends on what YOU feel safe doing.
If it worries you, don't do it!
Good luck.
