Just my $.02.
I would caution you on towing over your TV rating. In California (i know) the Highway Patrol has a division specifically for commercial vehicle enforcement. Since 99% of the pickup trucks on the road out here are registered as a commercial vehicle, they will stop, weigh and inspect a clearly overloaded RV as well. They wont care that you swapped your rear end, added air bags and a computer chip to eek out a little more HP and torque. They base it on the door sticker. Its a huge fine, not to mention you may get your entire rig impounded. Worse yet, if you get in an accident, your insurance company may not cover you at all, due to the overload.