That 2011 truck will last 300k at least. High miles really aren't an issue with the motor, but the rest of the truck will still age.
I have to agree, 40k on a 2012 with 10 miles is a better buy. Even if you had to fly to Seattle to get it.
With the bigger wheels, the on board computer doesn't know they're bigger unless it's been calibrated. So you have to figure the tire size error into your MPG calculations. The onboard computers are also notoriously optimistic.
As much as I love the looks of a slight lift and larger tires, they're going to do nothing for you except look good. Smaller, narrower, highway tires and a lower ride height will improve the fuel efficiency. I'm assuming you don't go too far off-road with the trailer.
Most AS folks like 2WD, but an interesting thing about 4x4 is that it holds it's value. If it's $3,000 more for the 4x4 new, it's $3,000 more for 4x4 when it's 5yrs old. Maybe not exactly $3k, but pretty close.
As much as I love diesels, there is a long break-even point on the added expense. You have to drive it over 150,000 miles (roughly) to realize the savings of owning a diesel. Those numbers change all the time with the price differential of gas/diesel, and the different manufacturer's cost of gas vs. diesel.
You should check out the 2014 Dodge 1500
3.0 diesel. After 15 years of hearing rumors of a 1/2 ton diesel making it to the USA, Dodge has officially announced an Italian made V6 3.0 for this fall. We're all hoping that this truck will hit the 30mpg highway mark. The rest of the world has mid-sized diesel trucks. If Toyota brought the Diesel Tundra to the US, I'd own one. I would have owned one 15 years ago.
I have another reason to own a diesel. I make my own biodiesel for about 25 cents a gallon. So the payback on diesel is much quicker for me. My truck gets about 16 commuting and around town, and the best I've gotten is 23 (22.9) on homebrewed B100, strictly hwy, no trailer, hand calculated, 0.7% odo error, on 35" tires and a 3" lift.
Good luck with the search. Let us know how it ends.