The Sierra HD and its twin the Chevrolet Silverado HD are designed for heavy towing and hauling.
The 6.0-liter V8 and 6.6-liter turbodiesel are both mated to a six-speed automatic.
The latter works well, and employs a heavy-duty Allison-made transmission.
We measured 14 mpg overall with the diesel.
The LTZ trim has a luxurious cabin but ascending to into it is quite a climb.