This page covers the complete technical specifications for the 2026 GMC Sierra 2500HD. For a plain-language look at the model, see the Sierra 2500HD overview; for a trim-by-trim breakdown and price ladder, see all trims and pricing. It is part of our Sierra 2500HD research hub. Pricing runs from $47,000 to $94,200 before destination across seven trims.

Powertrain

Engine Specifications

The Sierra 2500HD offers two engines, and only two. Both pair exclusively with the Allison 10-speed automatic transmission. The diesel is what unlocks the headline tow and payload ratings.

6.6L V8 Gas (L8T) — Standard

The standard 6.6L gas V8 (L8T) makes 401 hp and 464 lb-ft of torque. It is the standard engine from Pro through Denali and is enough engine for most heavy-duty buyers who are not towing at the maximum every day. Rear-wheel drive is standard on the base Pro; four-wheel drive is standard on the rest of the line.

6.6L Duramax Turbo-Diesel V8 (L5P) — Available

The available 6.6L Duramax turbo-diesel V8 (L5P) makes 470 hp and 975 lb-ft of torque. It is optional on every trim and comes standard on the Denali Ultimate, the only trim with the diesel included. The big low-end torque is what makes the Duramax the engine for grade climbing and sustained trailering.

Engine	Horsepower	Torque	Transmission	Availability
6.6L V8 gas (L8T)	401 hp	464 lb-ft	Allison 10-speed	Standard, Pro–Denali
6.6L Duramax diesel (L5P)	470 hp	975 lb-ft	Allison 10-speed	Available all trims; standard on Denali Ultimate

Footprint

Exterior Dimensions

Overall length depends on cab and bed. Width and height are consistent across the line. These figures come from GMC for the 2026 model year.

Measure	Value
Length, Regular Cab (long bed)	236.30 in.
Length, Double Cab (standard bed)	241.22 in.
Length, Crew Cab (long bed)	266.77 in.
Height	79.8 in.
Width (with mirrors)	105 in.
Width (without mirrors)	81.85 in.
Curb weight (unloaded range)	6,257 to 8,484 lbs
Fuel tank	36 gal

Cabin

Interior Dimensions

Seating is three across in the Regular Cab and up to six in the Double Cab and Crew Cab with the front bench. GMC advertises best-in-class standard Crew Cab front head and leg room for the Sierra HD, which is why the Crew Cab is the cab of choice for crews that spend the day in the truck. Exact head, leg, and shoulder room break out by cab and seat configuration; for the inch figures tied to a specific build, ask our product team for the window label on the truck you are considering rather than relying on a generic number.

Cab	Seating	Front room note
Regular Cab	3	Single row
Double Cab	Up to 6	Rear-hinged rear doors, smaller back seat
Crew Cab	Up to 6	GMC-rated best-in-class standard front head and leg room

Work Numbers

Capacity and Capability

Towing is published two ways, and they are not the same number. The gooseneck and fifth-wheel rating is higher than the conventional bumper-pull rating because the load sits over the rear axle. The headline figures require the Duramax and the right trailering package and configuration. For the full breakdown of hitch types and trailer matches, see the Sierra 2500HD towing and payload guide.

Capability	Rating	Configuration
Max towing, gooseneck / fifth-wheel	22,390 lbs	Reg Cab long bed, 2WD, Duramax, Max Trailering
Max towing, conventional	20,000 lbs	Crew Cab, Duramax, Max Trailering
Gooseneck max, Crew Cab	21,870 lbs	Crew Cab, Duramax, properly equipped
AT4 max towing	21,300 lbs	AT4, Duramax, properly equipped
AT4X max towing	18,500 lbs	AT4X (off-road hardware lowers the rating)

Payload depends heavily on cab, drivetrain, and engine, since a heavier diesel reduces what is left for the bed. The clean configuration-specific anchor is the AT4 4WD Crew Cab at 3,428 lbs. The off-road AT4X carries less, roughly 3,012 lbs with the gas V8 and about 2,822 lbs with the diesel because the lift, dampers, and skid plates add weight. Across the line, payload runs roughly 3,400 to 3,800 lbs depending on configuration; the lightest gas configurations sit at the top of that band.

Bed

Bed Lengths

Two bed lengths are offered: a standard bed at 82.3 in. and a long bed at 98.3 in. The Regular Cab comes with the long bed only. The Double Cab and Crew Cab can be ordered with either bed, and the AT4X is a Crew Cab short-bed truck. A 4-by-8 sheet of plywood lies flat in the long bed; in the standard bed it rides with the tailgate folded or stepped on the MultiPro inner gate.

Rolling Stock

Wheels, Tires, and Brakes

Wheel size steps up with the trim. SLE rides on 17-inch machined-aluminum wheels, SLT on 18-inch machined-aluminum wheels with dark grey accents, and AT4 on 20-inch gloss-black aluminum wheels with available BFGoodrich off-road tires. The AT4X swaps to 35-inch Goodyear Territory MT tires on its own wheels, with 18-inch Salta wheels available on the AEV Edition. Denali and Denali Ultimate use larger polished and painted wheels for a street-tuned look. Every trim runs four-wheel disc brakes with anti-lock control, and a Trailer Brake Controller is standard from the base Pro up, so the truck is wired to manage trailer braking out of the box.

Fuel

Fuel Economy and Range

The Sierra 2500HD does not carry an EPA fuel-economy rating. Heavy-duty trucks above 8,500 lbs gross vehicle weight are exempt from EPA fuel-economy testing, so there is no official city or highway figure to quote, for this truck or any of its direct rivals. Real-world economy depends almost entirely on load and terrain; a diesel HD running empty on the highway does far better than the same truck pulling a heavy trailer up a grade. The 36-gal fuel tank is the spec that actually drives range, and the diesel's efficiency under load is the practical reason many heavy trailer owners choose it. If a source quotes a precise MPG number for this truck, treat it as an unofficial estimate rather than an EPA rating.

Driver Aids

Safety and Compliance

An HD rear-vision camera is standard, and the trailering hardware is the heart of the safety story on a truck this size. Available driver aids include up to 14 camera views with HD Surround Vision and Transparent Trailer View, the ProGrade Trailering System with the in-vehicle trailering app (standard from SLT up), and available Adaptive Cruise Control with trailering. Denali Ultimate adds trailer tire pressure and temperature sensors. The cabin tech that supports it scales from the base 7-inch screen to a 13.4-inch central touchscreen with a 12.3-inch digital driver display from SLE up, and AT4 offers a 15-inch head-up display with an off-road inclinometer.

One clarification worth making: the Sierra 2500HD does not offer Super Cruise. That hands-free driver-assistance system is a Sierra 1500 feature and is not available on the heavy-duty trucks, so do not shop the 2500HD expecting it.

In Practice

What These 2026 Sierra 2500HD Numbers Mean in Practice

Around Hot Springs, those dimensions matter in two practical ways: squeezing a long-wheelbase three-quarter-ton into older garages and tight parking, and putting six to eight thousand pounds of curb weight onto soft lake-access ramps and the graded Ouachita Mountains backroads that Caddo Valley and Fountain Lake drivers run. Here is how these numbers translate to the daily reality of owning one.

The number	What it means for you
Width 105 in. with mirrors (81.85 in. body)	The body clears a standard 96-in. garage door, but the mirrors do not. Fold them for older single-car garages and automated car washes.
Length up to 266.77 in. (Crew Cab long bed)	At nearly 22 ft, the Crew Cab long bed will not fit a 20-ft garage bay or a compact stall. The Regular Cab long bed at 236.30 in. just tucks into a 20-ft bay.
Height 79.8 in.	About 6 ft 8 in., so it clears most 7-ft residential garage doors. Check posted clearances on parking decks, which are often lower.
Curb weight 6,257 to 8,484 lbs	A loaded three-quarter-ton sits heavy on soft ground and lake ramps, and can exceed posted weight limits on some decks and bridges. Plan the route when you launch a boat.
Bed 82.3 in. standard vs 98.3 in. long	A 4-by-8 sheet lies flat in the long bed. In the standard bed it rides with the tailgate down or on the MultiPro inner gate.
Long wheelbase	Expect a wide turning circle. Leave room in narrow lots and historic downtown parking, and favor pull-through spots when you are towing.

The short version: if it lives in a typical garage and runs the lake on weekends, the Regular or Double Cab fits more easily and the gas V8 is plenty. If it works all week and tows near the top of the range, the Crew Cab with the Duramax is the configuration to build, with the understanding that it needs the parking and clearance room that comes with the length. View the 2500HD inventory to see which cabs and engines are on the ground now.

Spec Questions

Specifications FAQs

Specifications are for the 2026 GMC Sierra 2500HD and were verified against the manufacturer's published 2026 specifications on June 28, 2026. Figures vary by cab, bed, drivetrain, and equipment; confirm the numbers for a specific build with our team at Allen Tillery Buick GMC.