For those who may be interested, Chevy & GMC trucks and SUVs (Suburbans, Tahoes, Yukons and I think the mid size models as well) which have 4-wheel drive, in recent model years to the current 2012 models, can disconnect the drive shaft electronically with just the twist of a knob - for 4-down towing.
The 2012 Chevy Avalanche LTZ we recently bought is a 4x4 version and with one twist of a knob it's ready to tow 4-down. Fantastic original factory option - no aftermarket modifications needed to do that. I believe these models have been this way for 5 years or so if you're looking for a used vehicle.
We're thrilled with the Avalanche LTZ... all the luxuries of a Cadillac and rides as smooth and comfortably as one also. √ We use the enclosed cargo bed of the Avalanche to store items like camp chairs, my bike, etc. out of sight-out of mind. That frees up a lot of cargo space from the basement of the coach.