It seems the folks over at GM are as experienced at emergency surgery as the cast of “ER.” Across GM’s entire lineup of cars, trucks and SUVs, the company has tried to enhance fuel economy above all else, often with significant results.

We can only report with certainty on the models whose EPA estimates have been reported so far, and the ones that stick out most are GM’s midsize sedans and full-size trucks.

The Chevy Malibu, Pontiac G6 and Saturn Aura now feature a six-speed automatic transmission in their four-cylinder models. The six-speed is offered only on certain trim levels of the Malibu and G6, but is standard, along with stability control, on the Saturn Aura. Prices haven’t been announced for the 2009 models, but prices for the same trims/packages for 2008 were $21,185, $21,775 and $20,405, respectively. That makes the Aura by far the value leader of the trio.

What does the new transmission mean at the pump? It means the trio — rated at 22/33 mpg city/highway, up from 22/30 mpg for 2008 — is now more efficient than four-cylinder versions of the Toyota Camry and Honda Accord, which are rated at 21/31 mpg and 22/31 mpg respectively. They even best the manual-transmission Accord at 22/31 mpg.

Earlier, we reported on both the 2009 Chevy Aveo and the 2008 Cobalt base models getting mileage bumps.

What other GM models get better mileage this year? The Chevy Silverado.

The 2009 Chevy Silverado pickup only saw an increase in mileage on its biggest 6.0-liter V-8, going from 13/19 mpg city/highway to 14/19 mpg for 2009. And while GM’s Chevy Tahoe, Suburban and GMC Yukon also get six-speed transmissions in models equipped with larger V-8s, estimated mileage remains the same as it was in 2008.