New car reviews

2015 GMC Sierra Denali 2500 HD

Massive Truck With Gigantic Capabilities

Jim Powell, Tue, 22 Jul 2014 01:53:26 PDT

I have driven many large pickup trucks over the years and own a 1-ton diesel DRW crew-cab truck now. However, a week in the all-new 2015 GMC Sierra Denali 2500 HD has convinced me that the bed in the back is about the only similarity between this huge luxury ride and my heavy duty workhorse. General Motors might have some huge mountains to climb as a corporation, but they have built a very impressive and capable truck to get them through the valley and up the next mountainside. Furthermore, there are more creature comforts in today's trucks- and the luxurious GMC Sierra Denali might just be king of the hill.

To begin, the ride quality in half-ton pickup trucks has improved immensely over the past several years in all the brands. These heavy duty pickups have ride qualities which vary greatly between Ford, GMC/Chevrolet, and Ram. I was expecting a harsh, pounding ride on LA freeways with our test Sierra 2500 HD 4x4 with 10-ply tires at 80 psi. Riding empty with a full tank of diesel, the trip was comfortable and controlled, even over the uneven pavement of the 405 Freeway.

GMC accomplishes the controlled ride under load and empty with a short-long arm/torsion bar front suspension and machined cast iron lower control arms. There are five different torsion bar rates for five different front gross axle weight ratings from the cushier Denali up to the snow plow-ready SLE and SLT models. The rear still uses an asymmetrical leaf-spring with a two-stage leaf-spring design on 2500HD models and a three-stage design for the 3500HD models.

Technology abounds in modern trucks for hauling huge loads safely. GM starts with StabiliTrak electronic stability control standard on all single-rear-wheel models and 3500HD dual-rear-wheel models. This includes their trailer sway control and hill start assist which holds the truck still while accelerating up a hill. The ABS and advanced collision systems all work seamlessly to control loads.

My only complaint against such a luxurious cab is that the interior insulates the driver so well that it is easy to forget how much weight is being transported. It is easy to go too fast, corner too sharply, and follow traffic too closely due to the lack of noise and vibrations. Drivers of modern big trucks are lulled into a false sense of stability. With torque-laden pulling power, the modern diesels generate so much speed, that loads can be out of control in a hurry. Big load haulers have to be extra careful not to run out of skill, pavement, or luck, or people are going to get hurt.

Our Duramax diesel powerplant included the diesel exhaust brake in addition to auto grade braking which controls truck and trailer speeds on the long downhill grades. Similar to aftermarket tuners, the diesel exhaust brake uses the turbocharger to create additional engine backpressure (in conjunction with the Allison automatic transmission downshifting) to help slow the vehicle.

GM's Isuzu built Duramax 6.6-liter turbo-diesel engine has seen a number of upgrades over the 14 years of production and is proving to be one of the most reliable diesel engines out there. The power is almost unlimited with 397 horsepower at 3,000 rpm and 765 lb.-ft. of torque at 1,600 rpm. There is a 6.0 liter V8 engine with a bi-fuel gasoline/compressed natural gas option, however, the pulling power of the Duramax is hard to pass up for the heavy hauler.

The Duramax includes a rigid cast iron cylinder block with induction-hardened cylinder bores; four-bolt, cross-drilled main bearing caps; forged steel, nitride-hardened crankshaft; aluminum pistons with jet-spray oil cooling; aluminum cylinder heads with four valves per cylinder; water-cooled turbocharger; integrated oil cooler and a charge-cooled turbo-charging system. Best of all, they have been tested to run 200,000 or more. If only GM would step up the warranty to match these claims!

The desirable Allison 1000 six-speed transmission is smooth and sure-shifting without hesitation under load. Furthermore, this transmission can be manually controlled by the driver with a push of a button for complete control in awkward driving conditions. Pulling loads out of mud, snow, or sand requires some manual control that only a human being can anticipate. Even with heavy duty hardware that can handle the massive torque, I found the Allison smooth and comfortable in all daily driving. Again, things are so smooth in the 2015 Denali, one forgets that this truck weights in excess of 7,200 lbs.

Our 2015 GMC Denali 2500HD with 4-wheel drive had a payload of 4,306 pounds and a maximum conventional trailer weight rating of 14,500 pounds. These are both up from the 2014 Sierra models. The maximum 2500HD fifth-wheel or gooseneck trailering weight is a huge 17,900 pounds - up from 17,800 pounds on previous models. Even with all this capacity, our Sierra 2500 HD 4x4 was maneuverable and had a good turning radius of 51.8 feet.

The new exterior design is bolder and yet more refined. The height of the hood and bed side rails make simple maintenance and load cargo a challenge but all levels of build quality are undeniable. The new grille design is massive and GM claims it enhances engine-cooling. There is more air drafted into the engine compartment to keep things cooler while towing on a mountain grade.

Similar to the 2014 Sierra 1500 - a new double cab body replaces the previous extended cab. It features longer, front-hinged rear doors with outside pull handles at the rear, for improved access in tight parking spaces. The dual cab has good openings for passengers and legroom for everyone. Shorter passengers will need a step or two to get into the 4x4 Denali 2500. Great ground clearance for rocks and ruts but the increased ride height needs some side rails for anyone shorter than 6 feet tall.

I do like the new GMC beds (box designs) with 6'6" and 8' lengths. They are stronger and more durable, easier to use, and offer greater cargo flexibility. They come with a two-tier loading design. Due to the smaller wheel well humps, these boxes also offer more than four feet of loading space between the wheel houses for standard 4' x 8' sheets of plywood and then some. The new "CornerStep" rear bumper is standard.

There are four trim levels which include a more reasonably priced Sierra Base model, as well as SLE, SLT and Denali. The distinctive Sierra Denali HD, which accounts for more than one-third of Sierra HD crew cab sales, is offered exclusively as a crew cab with room for 5 adults.

The new interior includes so many options but is centered around GMC's next-generation IntelliLink - with an eight-inch-diagonal color touch screen. The OnStar with 4G LTE enables greater connectivity than ever before, along with an available built-in Wi-Fi hot-spot (available in September 2014). IntelliLink serves as the main hub for Bluetooth-connected phones and portable devices connected through five standard USB ports. The toggle switches are coming back and GM uses them tastefully. Although, the logic of which switch is where is beyond me, i.e. traction, braking, and engine functions were mixed with lane departure warning systems and exterior lighting.

Most of the IntelliLink controls are accessible through GM's Natural Language Voice Recognition which is easy enough to use. I found it to be accurate most of time and fairly intuitive. Available IntelliLink connectivity includes Pandora and Bluetooth phone apps. The new maps in the navigation software are easy to read.

Other features standard on Sierra Denali include projector-style headlamps with light-emitting-diode (LED) signature daytime running lights, a Bose audio system, heated and cooled leather front bucket seats, a heated steering wheel and a power sliding rear window with defogger.

All 2015 Sierra Duramax-powered HD trucks get a step rear bumper, EZ Lift and Lower tailgate, locking tailgate, upper box tie-downs, StabiliTrak with Trailer Sway Control, cruise control, auto grade braking and diesel exhaust braking.

You might just need that truck bed to lie down in when making the first payment. Our test 2015 GMC Sierra Denali 2500 HD 4x4 with the Duramax package, 20" wheels, off-road suspension package, and camper package came to a huge $63,835. To be fair, this is the price range of all top-end pickup trucks today.

All 2015 Sierra HD pickups are assembled in Ft. Wayne, Ind. and Flint, Mich., and are backed by a GMC Pro Grade Protection. This "Pro Grade Protection" package includes two years of scheduled maintenance - including diesel exhaust fluid - a three-year/36,000-miles bumper-to-bumper warranty and a five-year/100,000-mile powertrain warranty.


Vortec 6.0L V-8 (L96 / LC8) Duramax 6.6L Turbo-Diesel V-8 (LML)

Type:6.0L V-86.6L V-8


(cu in / cc):364 / 5967403 / 6599

Bore & stroke (in / mm):4.00 x 3.62 / 101.6 x 924.05 x 3.89 / 103 x 99

Block material:cast ironcast iron

Cylinder head material:cast aluminumcast aluminum

Valvetrain:overhead valve, two valves per cylinder, variable valve timingoverhead valve, four valves per cylinder

Ignition system:coil-near-plug, platinum- tipped spark plugs, low-resistance spark plug wirescompression, glow plug start aid

Fuel delivery:sequential fuel injectiondirect injection diesel with high pressure common rail

Compression ratio:9.6:116.0:1


(hp / kW @ rpm):360 / 268 @ 5400

(L96 / LC8 w/ gas)*

301 / 225 @ 5000

(LC8 w/ CNG)*397 / 296 @ 3000


(lb-ft / Nm @ rpm) :380 / 515 @ 4200

(L96 / LC8 w/ gas)

333 / 452 @ 4200

(LC8 w/ CNG)*765 / 1037 @ 1600

Recommended fuel:regular unleaded (L96)

regular unleaded or CNG (LC8)*diesel or B20

Maximum engine speed (rpm):60003450 (powered)

4800 (braking)

Emissions controls:three-way catalytic converter, positive crankcase ventilation, evaporative collection systemcooled exhaust gas recirculation (EGR), EGR cooling-bypass system, diesel particulate filter system (DPF), selective catalyst reduction (SCR)



2015 GMC Sierra Denali 2500 HD

heavy duty interior

towing with the Denali

Duramax engine

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