This is just a rant thread - I'm personally tired of everyone saying "Oh no, gas is $3 a gallon, I'm going to have to trade in my truck" or "How can I increase performance AND mileage in my Tundra"
Bottom line is, you bought a Tundra, it's a truck, trucks do not get mileage on par with cars. I can appreciate folks trying to eek out every last ounce of fuel savings, but the best way to do this is not through truck modifications, but through changing your driving habits. Either cutting down on the trips you take, or going easy on the accelerator. Just about anything else is going to eat up the potential savings in the cost of the mod/time to implement the mod.
Trading the truck is just as bad of an idea. Cars are horrible investments, if your transportation is paid for, it will be almost impossible to recoup the cost of a new vehicle in fuel savings, esp. once insurance and maintenance (the whole "beater" idea) is taken into consideration.
So bottom line, a truck is a truck, don't buy one expecting high mileage, to get high mileage you would sacrifice what makes a truck worth having - strength, payload, durability etc. etc.
Just my .02
In conclusion
Don't buy a truck with/expecting high mileage, don't buy "low fat" snackwell cookies expecting them to taste like Oreos, and for Pete's sake, don't buy non-alcoholic beer, all defeat the purpose/benefit of the original and in the end - comparatively speaking, suck.