When we hauled 5500 lbs with our 97 dodge dually it was pretty much bottomed out on all 4 corners!
In addition to the 97 Dodge dually we also have a 97 F350 dually with a 7.3 Powerstroke. There is basically no difference in load capacity between our Ford and Dodge that I can tell. Both have 5 speeds and 300K miles. The Cummins is turned up and has at least 150 HP on the 7.3. All of us here wish the Ford was a Dodge, the cab and interior much nicer and roomier on the Dodge, and the Powerstroke 7.3 versus the cummins is not in the same league. Right now the 7.3 barely runs and needs $1200 worth of injectors.
I don’t think any of the 350 trucks other than these current trucks probably 5 years old or newer would handle those 5K+ Lb campers, and I am pretty skeptical that is a a good idea even on those new trucks that have enough payload rating. We also have a 88 F450 diesel, I think it would hold up those big campers, but it is a 450. It’s suspension and frame is built like a tank. Lol…it also rides like one. It rides so rough empty you get bruises from the lap belt when driving across across rough roads. I get a knot on my head from wearing a ball cap from my head hitting the roof.
We have replaced the pop metal bracing under the dash several times because it rides so rough it can’t hold the steering column up, fatigue cracks all over the cab. Ford tough. Lol