I would like to add my own two cents to Squid's excellent octane coverage. If you want to get better gasoline mileage with the 5.7 L, running premium gas WILL give you better mileage if you don't lead foot, if you coast instead of hard brake to a stop and if you accelerate mildly instead of neck snap. The 10.2:1 compression ratio used in the engine is way above the 8:1 compression ratio of most of today's vehicles that can run on regular gasoline. With this high compression ratio, the spark timing is controlled by the Engine Control Module (computer) up to the detonation point. The point is detected by the (4) detonation sensors located between each cylinder pair at the firedeck level. The Owner's Manual and the Service Manuals say to use 87 octane OR HIGHER. What that means is, if you run higher octane, the ECM will keep advancing the spark plug firing until detonation is detected.
Here in Michigan, octane is commonly 87/89/93. I believe that the use of higher octane will allow advanced timing and a resultant higher mpg. Since I haven't had my Tundra long enough to do detailed mpg analysis, I do not know if straight 93 octane or a less expensive mixture of 89/93 octane will cause the timing to advance to maximize mileage. However, at some point the ECM will not allow spark plug firing to advance any further, even at 100 octane. You might want to experiment with this, after all, it 's your dime. So, if I haven't bored you silly, max POWER and max MILEAGE are available with the SAME fuel, but your driving habits are the most important factor in increasing mpg.
On another note, I bought the TOYOTA TUNDRA 2007 Technical Features Manual on Ebay, and found more easily understood information on the actual workings of the various features (engines, trans, drivelines, options, brakes etc) than in the set of 6 Toyota Tundra Service Manuals that I have. I am not the seller of the new Features Manual, but if you would like some GOOD info, for 2007 through 2009 Tundras, I highly recommend this book. The publication is actually for the technical people at a Toyota garage before the new models come out. It is well worth the $35-$45 for the manual and I see they are still available on Ebay.
The only feature I don't like on my Tundra is the CRUISE light. I would prefer it lit ONLY when I have cruise activated, not when it is just enabled. There is my two cents. DRAYKS