Robert,
I have the same issue. With my camper on and the boat hooked up I was at 11,200 lbs . This was 5,200 lbs on the front axle and 6,720 lbs on the rear. A pretty sobering arangement to say the least. The door sticker says 8,800 gross, 5,200 front and 6,084 rear. I am over on gross and rear axle weights. Big shock here.
The truck handled the weight very well stock, to my amazement. I have since added the Ride Rite Air Bags and the Rancho RS9000 adjustable shocks. I pressure the air bags up to about 45 psi, when I have the boat hooked up about 30 psi when not. The RS9000's are set to max on the rear and about 7 on the front. I run 65 psi front tire pressure and 80 psi rear. My truck is the Heavy Duty model so it came stock with front and rear sway bars and the rear overload springs.
After some research, the axle ratings on the door sticker boiled down essentially to the tire weight ratings. With the tires inflated to a set pressure. As an example, the sticker reflects lighter tires than I have on my truck. I believe these were LT255/75 R16 which are rated for 3,042 lbs at 80 psi. Hence the 6,084 lbs sticker rating on the rear axle. The front axle sticker rating is 5,200 lbs, with a tire inflation pressure of 65 psi (from memory). My tires are LT265/75 R16 which are rated for 3,415 lbs at 80 psi (in the single rim configuration). These weight ratings are based upon tire pressure and driving speed.
I had read that for load capability you should stay within your sticker axle weight limits. Because my front axle loaded weight was quite a bit under the sticker weight I had some relief from worry there. The rear axle gave me alot of grief. So much that I almost went out and bought a 05 DRW, which for the Dodge had a sticker gross load rating of about 11,500 if I recall correctly. My truck is getting close to being paid for so this 25,000 dollar option sounded good at first, but soured quickly.
After more research, I found out my rear axle is the Dana 80 / 70 Full Floating Hybrid. This means it has the Dana 80 pumpkin and the Dana 70 axles. The bigger pumpkin because of the added torque of the Cummins. As best as I could discover the load rating was 7,500 lbs for this axle. So I could then say that the maximum rating would be 6,830 lbs which is the combined load capacity of both rear tires. With the scale weigh in at 6,720 lbs I am very close to this weight limit.
I spoke with a couple of tire dealers about upgrading my tires and rims to R19's. I really came down to about $ 2,000 for an additional 670 lbs weight capacity for the rear axle. Because I felt I should not exeed the mechical load rating of the axle. While talking to them, I also found out that most weight ratings for tires carry at least a 10 % safety margin. Which is built in to an already significant safety marging. The margin was more for better quality tires. This would realistically place the rear axle weight capacity at 7,513 lbs which is almost exactly the mechanical rating on the axle itself.
While running loaded, I checked my tires frequently for quite a period of time. On a 95 degree day, the tires would get warm, but not hot. So I was satisfied that they were handling the load and my driving speeds very well.
Now all this is fine and dandy, except for one problem which is a problem each owner like yourself must decide upon. The question is this "The truck can haul the weight OK, but can it stop the weight OK?". This question can only answered by that person hauling the weight. No doubt the stopping distance is significantly increased.
In my experience, it hauls the camper just fine. As long as I don't spend too much time gawking off at something and forget I'm at 13,000 lbs total weight driving at 60 mph. Of course, at those times I find that I occassionally need to check and see if massive adrenalin surges can make my throat fall out the bottom of my heart. My first clue often being when my GF, who seems to have a higher situational awareness, warns me of impending doom by a rapid intake of air.
You have to drive it 100% of the time.
Sorry for the length, I hope this gives you some usefull information to work with.
Jim