PickupTrucks.com has a new batch of 2017 Silverado HD spy shots via Brian Williams' SpiedBilde:
"This is the Chevrolet Silverado HD featuring the latest Duramax diesel engine, caught cold-weather testing in Michigan.

"GM is expected to give the Duramax diesel in the Silverado and GMC Sierra HD trucks a revamp in order to keep torque and efficiency competitive with the latest Power Stroke and Cummins diesels from Ford and Ram.

"Reports suggest the current 6.6-liter V-8 unit will be thoroughly reworked to dethrone the current Ford Super Duty in efficiency and hauling capacities, pushing it comfortably over the 425-horsepower mark, with at least 860 pounds-feet of torque. A heavy-duty eight-speed automatic transmission is also likely to become standard fare, but a 10-speed unit may not be far behind. No word yet as to whether Allison will continue as GM's HD transmission supplier.

"We've heard reports that the face-lifted HD trucks are supposed to last until 2020 or so, when the next-generation GM pickups will adopt a more aluminum-intensive structure to reduce weight as well as carry newly downsized engines for better efficiency and payload capacity is anyone's guess."
Look for the trucks to debut in time for the 2016 Texas State Fair in September.