I just read that Car & Driver article about the Tahoe and their 12mpg figure in spite of the 16/22 EPA numbers. Here's how they explained it:

"One obvious culprit for our poor fuel economy is our staff's desire to emulate drag racer Don "The Snake" Prudhomme. A less obvious culprit is the optional remote start that allows the key-fob possessor to start the engine from a distance. It's a valuable feature against bitter weather - the car can be warmed up in the driveway while you're waiting for that Pop-Tart to cool off - but using it means you're burning fuel and not going anywhere. We used it, a lot."