Need info 2007 Suburban

I am thinking about buying a 2007 Suburban 1/2 Ton model. Does anyone here own one who has kept track of the gas mileage?

Power is not important as I will get the smallest engine that they offer. It will only be used for vacations on the highway.

The window sticker says it will get 16 mpg (city) and 21 mpg on the highway but I wonder if that is true. My present suburban (1987 with 454 engine) gets 9 mpg on the highway.

Thanks

bought 2007 4WD (1500) about 2 weeks ago. City driving approx. 13 mpg. Not enough hiway miles yet to give accurate hiway mileage.