Truck

When we began fulltiming, we had a 2003 Ford F350 dually with the infamous 6.0 litre diesel. We owned the truck for six years, and put on about 50,000 miles of relatively trouble-free driving, mostly towing our previous fifthwheel, a 32 foot Keystone Laredo.
Despite the dismal reputation of the 6.0 (often referred to as the "six-point-Oh!"), we had no engine problems during the time we owned the truck. I believe that two factors contributed to this...almost all driving was highway towing mileage where the engine was working hard, and we changed the oil every 3000 miles using synthetic.
We purchased our Pinnacle in 2011, and made one return trip to California using the Ford as a tow vehicle. It was quickly apparent that the truck was operating at its limits hauling almost 16,000lbs. Braking was barely adequate, and the truck tended to be pushed around by the trailer, even with dual rear wheels. We made the decision to replace our tow vehicle, and began looking around and doing research.

The new and the old.

We made the decision to purchase a 2013 GMC Sierra 3500HD dually with the Duramax/Allison combination, mainly because of the solid reliability record of this powertrain. Our decision was helped along by the excellent deal we were able to make, even though the truck was factory ordered to our specifications. It was built in Flint, MI, and took about six weeks from order to delivery.
We ordered a black 2wd crew cab, in the SLT trim level, which included leather buckets and Bose audio, among other things. We decided to go with 2wd after much soul-searching, and after two years, have not regretted this decision. We have been in snow twice, and with almost 4000lbs pin weight over the rear wheels, traction is not an issue. If we intended to drive the truck unloaded in a winter climate, we would have decided differently.

A twinge of sadness! The Ford served us well.

The GMC is an invincible tow vehicle. It handles the trailer weight with great confidence, braking is very powerful and feels safe, and the chassis is never pushed around by the 40 feet of trailer following behind. Engine torque through the six-speed Allison is much more than adequate for our combined weight, and we have never encountered a highway grade that slowed us down. The exhaust brake controls the weight with authority, and we can descend the steepest interstate mountain downgrades without using the brake pedal, maintaining speed with the exhaust brake alone.
I have not yet felt a need for rear airbags with this truck. The rear suspension squats about two inches when the pin weight is applied, solidly onto the second stage of the three-stage leaf springs. This levels out the truck, which is slightly tail-high when unloaded. I did replace the OEM rear shocks with Rancho 9000XL adjustable units, after twice destroying the piston seals in the inadequate original shocks, which were replaced under warranty the first time.
Would we buy this truck if we were doing it again? In a heartbeat!

UPDATE: February 2016
I added airbags to the rear suspension last summer. On certain undulating road surfaces, the 16,000 lb mass of the fifthwheel, as it rocked fore-and-aft about the axles, seemed to exert so much vertical force that I found it annoying. It was not alarming or dangerous, just annoying.

I purchased a set of AirLift 5000 lb capacity bags, and performed the installation myself. It was a straightforward install, and took about 4 hours. I did not use an automatic compressor setup. I connected the bags together with a tee, and brought the air line to a fill valve located just inside the tailgate on the passenger side. I installed a pressure gauge next to the fill valve. I have a 3hp compressor permanently installed in the bed of the truck, powered from the onboard generator, and I use this to inflate the airbags before towing.

With the 3900 lb pin weight applied, the truck returns to its original ride height with 75 psi in the bags. After road testing with the fifthwheel attached, I found that the optimum pressure is 50 psi. The effective rate of an air spring increases with deflection, and this property limits the downward travel of the rear suspension when towing.

The porpoising effect mentioned above is great;y reduced, and the rig feels extremely solid and well-balanced. It was worth the $400 cost and the four hours work.