02/07/2008 11:06. I came to a stop at the light and watched the tachometer drop to zero as my GMC Sierra stalled. Yikes. I'm in thick traffic. Now what? Then I remembered, I'm in a hybrid and that's what hybrids do. Though this Sierra acts and looks just like its gasoline-powered cousin, like all hybrids it shuts down at standstills to save on fuel and prevent noxious emissions. Yet unlike smaller hybrid vehicles, this full-size pickup always seemed to need the gas-powered engine to move. As a result, its fuel-efficiency numbers aren't astounding: 17mpg city versus... // Newsweek