GM has widened the availability of its bi-fuel gasoline/CNG powertrain and revamped the exterior and interior design for the 2015 model year HD editions of its Chevrolet Silverado and GMC Sierra full-size pickups.

The heavy-duty stablemates entered production this month at GM plants in Fort Wayne and Flint.

“The 2015 Silverado and Sierra are major updates on trucks that were all-new under the skin [with a new chassis design featuring fully boxed frame] for 2011,” explained Jeff Luke, GM’s executive chief engineer of trucks, at a media rollout event held here this week.

“Our focus was on making the new Silverado and Sierra HDs stronger, smarter, more refined, and more confident across the entire lineup.”

Luke pointed out that many of the new HD enhancements first appeared on the 2014 Silverado and Sierra 1500 models. He noted that sales of those light-duty models got “off to a strong start” as they were up 16% last year and that the new-model changeover was “smooth” with 98% of December sales being for the new model.

Turning back to the 2015 HD roll-out, Luke pointed out the importance of the segment. He said more than 25% of full-size pickups sold in the U.S. are rated heavy duty, amounting to over 475,000 vehicles in calendar year 2013. He added that “about two-thirds of HD pickups are diesel-powered with most of these used more for personal use than [for] work.”

Along with providing strong brand differentiation via unique hoods, headlamps and chrome bumpers, Luke said the new HD exteriors improve aerodynamic flow for a quieter cabin and increased efficiency as well as an enhanced cooling effect for more consistent power.

“The sealed front end uses cooling air more efficiently and the engine air intake is isolated from the hot engine compartment to keep intake air cooler,” he explained. “This helps maintain full power when hauling or towing in high ambient temperatures.”

Under the hood, buyers can opt for one of three powertrains:

  • Duramax diesel mated to Allison 1000 Series six-speed automatic transmission. The diesel is rated 397 hp with torqe output of 765 lb-ft.
  • Vortec 6.0L V-8 rated 360 hp with torque output of 380 lb-ft; mated to six-speed GM automatic transmission
  • Bi-fuel CNG/gasoline setup (available on 2500 and 3500 models in all three cab styles) that boasts a separate CNG fuel tank to enable alternating between fuels “at the flip of a switch.” The CNG fuel systems are fully warranted and validated by GM, including a five-year/100,000-mile powertrain warranty, and sold and supported by Chevy and GMC dealers. It was noted also that all components will have GM service part numbers for “broad availability” on the road.

The 2015 HD trucks offer both increased payload and towing capabilities. Per GM, the models deliver “best in class” payload of 7,374 lbs and conventional towing of 19,600 lbs with factory hitch. Fifth-wheel towing is rated 23,200 lbs.

According to Luke, both towing and hauling benefit from fully integrated cruise control and Auto Grade Braking as well as the Diesel Exhaust Brake on Duramax-powered trucks that help drivers “maintain a more even speed up and down grades.”

He noted that the Diesel Exhaust Brake uses variable turbocharger vanes to generate backpressure for smoother, quieter operation as well as to prolong brake life and help prevent brakes from overheating

An integrated trailer brake control automatically detects and adjusts for electric-over-hydraulic trailer brakes. The OEM’s Hill Start Assist feature helps prevent roll-back on grades and its Hill Descent Control uses the truck’s ABS to control speed on steep down grades, both when running on and off-road.

HD safety features outlined by Luke included making StabiliTrak with trailer sway control standard on all 2015 HD pickups, including 3500 duallys.

In addition, the OEM offers Forward Collision Alert, Lane Departure Warning, a Safety Alert Seat, rear backup camera, front and rear park assist. Side-curtain and seat-mounted side airbags come standard on 2500 models and is available on 3500 models.

Moving inside, Luke stressed that a key design goal was “to bring the same level of refinement” to HD pickups that the interiors of GM’s light-duty pickups gained in the prior model year's revamping.

“The HD cab is all new,” he related. “It makes extensive use of high-strength steels. It features hydraulic body mounts for reduced noise and vibration, inlaid doors and enhanced aerodynamics for reduced wind noise and triple door seals for a quieter cabin.”

The all-important pickup box has also been upgraded. A big change here was adding the CornerStep rear bumper that was introduced on 1500 models in 2014. “It makes for easier access to cargo, which is even more useful on HD pickups due to their higher ride height,” Luke observed.

Other HD box news include the EZ Lift and Lower tailgate 9which is dampened) as well as availability of new upper tie-down points and under-rail LED lighting along with factory-installed spray-in bedliners.