I also have a 2006 3500 auto 4x4 with 93,000 miles. I bought a new fifth wheel RV weighing anywhere from 14,000 to 16,000 lbs.
The truck pulled it fine, but stopping was scary! I had a new PACBRAKE installed because an added benefit was having an air chuck on board with 130psi of air pressure. Pacbrake also gives you air hose, chucks, etc. to help you with a flat tire. Because of the increased compression I also had the head studded. The only remaining weak link is the flex-plate, and when things allow I am replacing it with a BILLET flex-plate. In summation I should have done this many years ago. I can't believe how the truck with or without the RV stops now, its incredible!
I know this does not answer your question, just know that this PACBRAKE is fantastic. Its worth your money!!!!