If you’re looking for obvious visual differences that separate the 2017 GMC Sierra HD Duramax from its 2016 predecessor, there is one main tip-off: a new hood scoop. That might not sound like much, but that scoop sits atop the ’17 Sierra HD’s biggest news: a revamped 6.6-liter Duramax V-8 diesel engine that cranks out class-leading horsepower.
The new-for-2017 Duramax (dubbed L5P in GM’s engine-coding system) is rated at 445 horsepower and a whopping 910 lb.-ft of torque–increases of 12 percent and 19 percent, respectively, over the previous Duramax 6.6. Ninety percent of that torque arrives at a usefully low 1550 rpm, and remains up to 2850 rpm.
Ninety percent of the L5P’s parts are new—they include a stronger cylinder block and heads with increased oil- and coolant-flow capacity, electronically controlled turbocharging system with higher maximum boost pressure (28 psi), direct-injection fuel system with higher capacity solenoid-type injectors, integrated oil cooler (with 50 percent greater capacity than the previous engine), and a full-length damped steel/aluminum oil pan. The new oil pan works in concert with new rocker cover/fuel system acoustical treatments and other sound-control measures to make the new engine significantly quieter than before—GMC says idle noise has been decreased from 86.7 dBA to 64.8 dBA.
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And, that previously mentioned hood scoop is for more than just looks. It’s a fully functional, patent-pending design that funnels cool air to the engine for better performance in heavy load, high-engine/transmission-temperature driving conditions. The “patent-pending” part is a clever arrangement of underhood ducting designed to keep water droplets and other unwanted matter from entering the engine intake.
The Duramax’s lone transmission is again the Allison 1000 6-speed automatic, but it’s been upgraded with a new torque converter and other updates to handle the engine’s higher output. Likewise, driveline upgrades such as a stronger front prop shaft and bigger U-joints were added, and the diesel emission fluid (DEF) tank’s capacity has been increased.
We drove the new Sierra HD Duramax on a press event that took us from the snowy, high-altitude conditions of Telluride, Colorado, to the desert-like climate of Paradox, Colorado—80 miles to the west and slightly north, near the Colorado/Utah border. There are plenty of steep grades, winding mountain roads, and high-elevation climbs in that neck of the woods, and the Duramax handled them all without breaking a sweat—even when loaded down with some heavy cargo.
All of the Sierra HD Duramaxs we tested were topline Denali models, which come only as crew cabs. GMC says that more than 90 percent of the Sierra Denali HDs sold are equipped with the Duramax diesel engine. Standard Denali amenities include wireless phone charging, remote-locking tailgate, heated steering wheel, heated and ventilated front seats, OnStar 4G LTE WiFi capability, and GMC’s IntelliLink touchscreen audio system with navigation and Apple Carplay/Android Auto functionality. New for 2017 is GM’s Teen Driver monitoring feature, which allows parents to view vehicle data such as top speed, miles driven, and the number of times active safety features were engaged during a drive. Standard safety equipment on Denali HDs includes Lane Departure Warning, Forward Collision Alert, Safety Alert Seat, and Front and Rear Park Assist.
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Also new for 2017 is an All Terrain X HD package available on SLT models in either Black Onyx or Summit White. It includes 18-inch black aluminum wheels, Goodyear Wrangler Duratrac MT-rated tires, Z71 off-road suspension, Rancho twin-tube shocks, black side steps, a black bed-mounted sport bar, spray-in bedliner, and unique interior and exterior trim.
During our test drives, we noticed some diesel clatter at idle and a pronounced, muscular growl in fast acceleration, but the Sierra HD Denali’s cabin was impressively quiet overall. Ride quality is quite good for a large pickup, though there is some telltale body-on-frame shudder over some bumps and pavement imperfections.
As expected for a line-topping luxury model, the Denali boasts classy interior materials—the contrasting stitching and leather-wrapped steering wheel were especially nice. Maybe we’re too soft for a truck like this, but we wished for push-button-start feature, like the Ford Super Duty trucks offer. On the plus side, the 4G LTE WiFi capability was a real godsend in the mountainous terrain of our test-drive route, where reliable cell-phone reception was often hard to come by.
Though the Sierra HD’s maximum towing capacity is 20,000 pounds with a conventional trailer and 23,300 with a fifth-wheel setup, GMC engineers say they were not chasing class-topping “bragging rights” towing numbers in the development of these pickups—rather, the focus was on all-around towing confidence. GMC engineers aimed at satisfying the majority of buyers who tow with their heavy-duty pickups—and research shows that those customers usually tow around 15,000-18,000 pounds.
GMC provided some loaded-up Sierra Denali HDs so we could test their towing and hauling prowess. We drove a 4WD 2500 model that was carrying two snowmobiles over its cargo bed (total weight—1150 pounds) and a 4WD 3500 dualie that was towing a fifth-wheel camper trailer that weighed 7200 pounds.
Both pickups handled their loads with aplomb, and we also appreciated the Sierra HD Duramax’s handy towing-assist features on our drives. The exhaust-braking system—which uses engine compression and backpressure from the variable-vane turbocharger to help slow the vehicle on sharp descents—provided piece of mind when hauling that camper trailer down a steep hill. The trailering camera feature was another great help—press and hold the “back” button below the IntelliLink screen, and a camera menu pops up that allows you to choose left- or right-side camera views, a pickup-bed view that’s helpful for connecting a fifth-wheel trailer, or a trailer camera if your trailer is so equipped. The left and right camera views can be combined, and the pickup-bed camera can be added for a two-way or three-way split-screen view. There are other subtle, thoughtful touches as well—when in towing mode, one of the gauges in the instrument cluster’s digital readout changes from battery charge to transmission-fluid temperature.
None of the incredibly capable diesel engines on today’s heavy-duty pickups come cheap, and the Duramax is no exception. The “Duramax Plus” diesel engine package was priced at $9255 on the 4WD Denali 3500 Crew Cab Dualie we tested, and $9550 on the 4WD Denali 2500 Crew Cab we drove (the price difference is because the 2500’s package included a power-adjustable heated trailer mirrors that are already included on the 3500 dualie). Both packages included a $750 discount that dropped the price into the $8K range, but the Duramax is still one pricey powerplant.
The Sierra HD lineup’s base prices range from $33,990 to $58,995 when equipped with the standard 360-hp, 6.0-liter gasoline V8. The total MSRP on the 3500 dualie we tested was $69,640, and the sticker price on the 2500 topped the $70K mark at $70,540. Extra-cost options such as Deep Garnet Metallic paint ($395), off-road suspension ($180), and roof marker lamps ($55) helped push the 2500 past the 3500. Note that while our press drive was focused exclusively on GMC trucks, the Sierra HD’s Chevrolet sibling, the 2017 Silverado HD, also offers the new Duramax engine and most of the Sierra’s features in a slightly cheaper, slightly less-upscale form.
For the select group of customers who need the heavy-hauling/towing capability it offers, the GMC Sierra HD Denali Duramax offers a high level of get-the-job-done functionality along with a surprising degree of overall refinement.
