The Silverado HD (and its twin, the GMC Sierra HD) first went on sale about 18 months ago, but GM is giving the truck a mild facelift that hints at major revisions happening under the hood.

Even with plummeting truck sales and fuel prices sky high, General Motors' heavy-duty pickups have to keep up with changing federal regulations and competitors. Here are the first pictures of a 2010 Chevrolet Silverado 2500 Duramax diesel test mule.

The Silverado HD (and its twin, the GMC Sierra HD) first went on sale about 18 months ago, but GM is giving the truck a mild facelift that hints at major revisions happening under the hood.

The grille in these photos is temporary, snagged from a current light-duty Chevrolet Silverado 1500, but the revised front bumper is production ready. GM has simplified and toned down the 4 piece front bumper assembly with huge chrome bumper end caps of the 2009 Silverado HD with a simpler 3 piece assembly with single chrome facebar, lower plastic valance and upper plastic filler pannel that extends the whole length of the facebar.

The inlet opening in the middle of the front bumper facebar, which feeds air to the truck's transmission oil cooler, is about 1/3 larger than the current inlet and hints to possible changes GM has planned for the Silverado's Allison transmission.

The Allison tranny is mated to the 6.6-liter Duramax diesel engine, which will be overhauled to meet tough new EPA rules for NOx emissions that go into effect on January 1, 2010. The bigger inlet could mean the next-gen Duramax will require additional airflow for a new exhaust gas recirculation (EGR) system, which reduces NOx, but GM has officially stated 2010 Duramax NOx emissions will be scrubbed using urea selective catalytic reduction (SCR). Using urea SCR should require a less complex EGR system.

Spy sources suggested that GM and Allison are planning to add extra gears to the current 6-speed Silverado for improved fuel economy and towing efficiency, perhaps, in the form of an 8 speed, like some luxury cars already have. Probably unlikely, however, extra gears would likely require improved airflow to the transmission oil cooler, and thus a bigger inlet in the front bumper. Also, extra gears could also allow give the Silverado an advantage over new heavy-duty pickups from Dodge and Ford, expected to arrive by 2010 and 2011, respectively.

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2010 Chevy Silverado Heavy Duty Spied with Front End Changes