Wiser folks than me have said, "You'll never want less tow vehicle. Consider that strongly since you are close enough to any variety of mountain experiences. Now did they say the redesigned 2007s wouldn't be out until early 2008?
Member barkingspider found that the more recent Tundra crew cabs had the highest capacity. In addition to tow capacity, pay attention to published payload or load capacity of the tow vehicle itself. This is the max limit of weight you want to put onto your tow vehicle. Load capacity is posted for a vehicle and trim level if so specified; all options you buy after that must subtract from this number (including hitch parts). The remaining load capacity must be enough for everything you need to put on the truck -- driver, passenger(s), topper/tonneau, gear or toys in the box, and hitch weight of your trailer.
Airstream's published number of hitch weight also applies to the basic model; options are extra. Many things that disproportionately weigh down the ball because of their location are LP gas, weight distribution gear, and spare tire (if you opt for the LS package). So actual tongue weight can easily be 200# more than the published...
But ... welcome to the Forums and really, really enjoy!!