Most states should have an exception from weight on personal RV's. Here in Montana the concern is length when pulling a boat or atv trailer behind the camper or 5th wheel. Also anything over 3000 lbs better have breakaway brakes on them. I pull doubles quite often. I only have a 19' fifth wheel with the atv trailer pulled behind it. This will be the first year for the NEW 07 2500 Hemi pulling. I just got rid of my 02 1500 QC 4.7 and pulled the same stuff with it. Hills were slow goin'.
I was going to change to 4:56 gearing in the 1500 but the 4 wheel drive option hampered that due to the $800 per axle replacement charges. Easier to change the truck.

 

At 70 m.p.h., in fifth gear, the r.p.m. is about 2,100. I have LT315/70R-17 (34.5") tires.

 

I'm about in the same spot, my 35" Cepeks actually measure closer to 34.5" and I'm right at 2100 rpm at 70 mph with my 4.56 gears...