Well get used to it.

It was the same with my 05 AC 4x4, other people were posting figures well over 20 MPG and my 05 would only get 15 or 16 on the highway, no matter how easy I drove it, that's all it would get. Don't count on any huge improvement after breakin either, it will be minimal. Then you'll hear, just like I did, "there must be something wrong with your truck"

Anyway it looks like the 07 Tundras are just like the 1st gen models as far as mileage goes, some will really shine and others will just be stinkers. I guess you got a stinker just like I did. Don't know why, that's just the way it is.