PHOENIX, Ariz. -- The I-17 multi-slab climbs out of Arizona's cactus-littered Sonora Desert at Phoenix to reach dense forests of tall pines in the Weaver Mountains, and we're taking this 50-mile uphill slog on I-17 to sample the fire power and tire traction of Chevrolet's Silverado 2500HD in a new 2015 iteration.
The "HD" initials signify Heavy Duty and describe a vast line of big and powerful work trucks developed by General Motors for the upward expansion of Chevrolet's full-size line of Silverado pickups.
Dressed in new sheetmetal with revamped truck beds, revised cab designs and downright plush cabin content, the Silverado 2500HD and 3500HD trucks for model-year 2015 emerge on high-strength chassis to enhance the ride and handling with stronger suspensions and beefy brakes, options for two powerful engines and overall boosted capacity to perform truck-tough chores with best-in-segment payload capability of 7374 pounds and maximum available tow ratings also climbing to the top of class -- 19600 pounds with a factory hitch and 23200 pounds for fifth-wheel towing.
In size-wise sequence Chevy's big trucks begin with Silverado 2500HD, which differs from a light-duty Silverado because it rides on the stronger and longer HD chassis and pulls from one of two engines tapped for HD service.
The base Silverado 2500HD WT (Work Truck) has the shortest wheelbase of the series -- 133.6 inches. It installs a regular-size 2-door cab and carries a pickup box that measures 97.8 inches in length.
There are choices for a gasoline-driven Vortec V8 engine or a Duramax massive-torque turbo-diesel V8. Both rear-motivated 2-wheel-drive and 4-wheel-drive traction modes apply.
GM's Vortec 6000 6.0-liter V8 serves as the gasoline-swigging plant. Output tallies to 360 hp at 5400 rpm, with torque skewed to 380 lb-ft at 4200 rpm. This engine ties to a heavy-duty Hydra-Matic 6L90 electronic automatic transmission with six forward gears.
The Duramax 6.6-liter V8 direct-injection turbo-diesel engine makes 397 hp at 3000 rpm and torque of 765 lb-ft at only 1600 rpm. The diesel links to a 6-speed electronic automatic Allison 1000 transmission which has a high-tech transmission control module to select gears and engage the torque converter lockup.
Chevy's Silverado HD trucks offer three cab styles -- Regular Cab (two doors and a bench or buckets), new Double Cab with two forward-hinged rear doors (bench or buckets in front of a back bench for three), and Crew Cab (4-door cab with front buckets or bench and big 3-seat back bench).
There are two different lengths for the rear truck bed -- 6'6" (78.9 inches) and 8' (97.8 inches), each with CornerStep bumpers and EZ Lift-and-Lower tailgate.
Silverado 2500HD and 3500HD trucks are constructed on fully boxed steel frame rails using high-strength steel. The suspension -- independent front with forged steel upper control arms and cast iron lower control arms plus torsion bars in place of springs to facilitate trim height adjustments, and rear asymmetrical multileaf springs -- produces a remarkably smooth ride quality.
The power-assisted Hydroboost brake-apply system installs a disc at every wheel with electronic linkage to a 4-wheel anti-lock brake system (ABS) with GM's StabiliTrak electronic skid controls plus standard Trailer Sway Control on all models including 3500HD dual-rear-wheel models.
An optional Z71 off-road suspension package adds Rancho monotube shocks on 2500HD, plus Hill Descent Control, underbody shields, brushed-metal door sill plates, a Z71-logo gauge cluster, special interior trim, unique front bumper and grille, and Z71-logo graphics on the cargo box.
Chevrolet trims the 2015 Silverado 2500HD and 3500HD trucks as WT (Work Truck), LT and LTZ, plus a new high-end version, Silverado High Country HD Crew Cab.
Unique gear for Silverado High Country HD includes a big chrome-bar grille, 6-inch tubular chrome assist steps, 20-inch polished aluminum wheels for 2500HD, saddle brown cabin trim with heated and cooled perforated leather seats, MyLink connectivity with 8-inch touch screen, Bose premium audio kit and front/rear park assist system.
Options range from a navigation system to a sunroof, rear-seat entertainment system with BluRay/DVD player, and a High Country Premium Package with heated steering wheel, driver alert package and power adjustable pedals.
The bottom line: Chevrolet's 2013 Silverado HD trucks carry MSRP figures rising from $31,500 to $52,500.