[rickst29]

Many, perhaps a majority, of small 2006 models (2619 and 2720) were built with 14" wheels. Late in 2006, TM made the following changes:
Lift kit is always present; 15" wheels and tires; and (perhaps?) a somewhat stronger axle. The early 2006 axle had a weight capacity of 3500 lbs.

It is quite easy to upgrade the wheels and tires; somewhat harder to install the lift kits (if needed); and "major work" to replace the TorFex axle. I don't know of anyone who has replaced the Torflex on their own. That would require a factory visit or an extremely capable maintenance facility.
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In short, the 2011 definitely has the running gear which you want. A used 2006 may or may not have upgraded wheels/tires and the lift kit already added, or it may have been built late in the year - but if it's an "early" one, even with owner-upgraded wheels and tires, it still has somewhat less cargo capacity. And two of the 3 beds in the 2619 are always "up and out", whereas two of the 2720 models have more room for people who don't need 3 beds.

As you see from my Sig, my own 2006 (one of the very first for that "model year") was built "custom", with much stronger suspension and 15" wheels/tires. TM decided to make most of my Running Gear changes standard equipment on all 2619 and 2720 models, and they've kept that change in place ever since.