I've got an 08 but not 4wd. Average I'd say 15mpg. I think your estimate is right on the lower end. The only time I've ever got 18 was 55-60mph for a full tank. That being said my next truck will be another Tundra. It's built like a tank, looks good, comfortable for all day driving, and I love it. I bought it knowing I'd get 15mpg and I'm ok with that.

I believe if Toyota enters the on road diesel market in the US they are going to have to kiss a certain amount of the "LEGENDARY DEPENDABILITY" history goodbye, the emissions systems are problematic.

I agree. Part of the reason that Toyota has such a great reliability record is because they don't seem to "push the envelope" as much as the big 3 do in terms of new engine tech. Toyota is running a big V8 that gets pretty lousy mileage to get the same type of performance the others are getting from much smaller engines with 20%+ better mileage. When you start adding new tech to increase output and fuel efficiency, there will be growing pains and issues to work through. If I was Toyota, I think I'd just continue trailing a decade or two behind on tech and continue using proven and time tested components and just maintain my reliability record. There is definitely a market out there for less cutting edge(drivetrains-wise) but more reliable trucks, as can be seen.

It is not just the engine technology but the higher gear ratios. Final drive ratios in Tundras are 3.91 to 4.30. Also from all the MPGs I have seen the Tundra gets much closer to the posted numbers that the others not counting diesels of course. Resale value will probably cover the difference in MPGs over 4 years.

My 08 gets 14ish with 35s and sittin a little higher. It's a 4.7.