Now that General Motors has the 1500 series of its new full-size trucks launched, the focus is on the upcoming debut of the 2500 and 3500 HD models. We caught these images of both 2500 and 3500 dualie models testing near Death Valley, California, one of the hottest places in the United States.

While the 1500 models are all-new models with new chassis, some of the HD models' chassis hardware is expected to carry over, as the trucks received an externally minor, but functionally significant, update in 2011 with new, heavier-duty frames, and the debut of the fifth-generation LML 6.6-liter Duramax turbodiesel V-8.

Now, the HD models will get the exterior and interior makeover that the 2011 update largely ignored. As expected, the spy shots show the overall design inside and out largely echoes that of the new 1500 models, with larger, more prominent fender flares and what appears to be a slightly higher hood. Likewise, the interior shows a strong resemblance to that of the 1500 models, and expected to be nearly identical in trim and features.

In terms of powertrain changes, the gasoline engine offerings on the HD models may adopt direct-injection, like the 1500 models, boosting horsepower, torque, and fuel efficiency. It's unknown if displacement will remain at 6.0 liters, or if it will get a 6.2-liter V-8 similar to the top-trim 1500 models. The Duramax diesel V-8 is expected to remain at 6.6 liters, but may get a bump in output to match the Ford 6.7-liter "Scorpion" Power Stroke V-8, and the updated Cummins 6.7-liter I-6 in the 2013 Ram HD models , some versions of which produce as much as 850 lb-ft of torque. Production is expected to start in late fall 2013, with the trucks rolling into showrooms in early 2014.