I have an 07 Canyon CrewCab Z71 4x4(3.7L w/4spd auto)
I got it in November and have put just over 3000km on it.
1 highway trip of 500km and the rest has been city driving.
I have gotten 15.1mpg overall so far on this truck.
I think this is alright as I am driving almost all city and almost all 4x4 engaged.
I expect it to improve as the engine breaks in further, the gas stations switch back to summer blend fuel and the snow melts so I will use the 4x4 far less.