Hey sorry for not being able to reply right away, but I do appreciate all the information you've been sending out here.
I should also say that I have mostly read online forums in the past and have seldom contributed so please excuse my lack of forum etiquette, I've got big feet and am bound to step on someone's toes.
Let me clarify a what I have: When I originated this thread I was contemplating purchasing this vehicle and finally decided I couldn't let it pass. I bought a former ambulance 2010 E450 with Advanced 4WD Systems 4WD conversion, 6.0 diesel, dual rear wheels, with just under 21k miles. Vin decoder indicates 4.56 gears, door tag code says should be 4.10 but I still need to confirm with the axle tag.
Right now is just a cab/chassis but I am in the process of installing a 42" cab back from Blackhawk cabbacks, with the intent to install an aluminum flatbed/hauler type of body. With the extended cab installed I should have very close to 10' of frame left. Distance from rear axle centerline to rear end of frame is 65"
The future intention is to hitch pull our 30' camper while having a 1500lb side by side UTV on the flatbed.
Back to the original towing question - I installed a hitch, seven way plug, Tekonsha TBC and towed my camper 150 miles each way July 4 weekend and it towed well. Roads/hills of NH are probably no comparison to the Rocky's but there are a couple places where the truck struggled, as I expected it would. I completely understand the weight limits of our vehicles and even if I am at the max combined weight, trailer brakes and weight distributing hitch make a world of difference, and I do have both. I intend to get the truck/camper weighed in the near future, I will post here when I do.
Thanks again for all your input, I look forward to posting here more often. Pics coming soon too.