The Sierra HD models are the mid-level part of GMC's truck lineup, so if your hauling happens once or twice a year, or you tow a bass boat or ski boat or a lightweight car trailer, then the 1500-series is better suited.Conversely, if you've got a mammoth trailer to pull, step up to the Kodiak/Top Kick medium-duties.However, if your trailer needs range 5,000-13,000 pounds, then a Sierra HD just might be the hot ticket.

The GMC Sierra HD pickups were thoroughly redesigned for 2007, so changes for 2009 are limited to detail changes: OnStar 8.0 with turn-by-turn navigation and destination download, Bluetooth wireless connectivity for your cellphone, XM Satellite Radio with real-time traffic information, rearview cameras for maneuvering in tight quarters and hooking up trailers, and electronic stability control expanded to more models.

The GMC Sierra HD offers styling unique to GMC, so it's a little more than just a Chevy Silverado with a different grille, but they're based on the same structure, use the same drivelines, and are for the most part mechanically identical.

As with all heavy-duty pickup lines, the Sierra HD offers plenty of configurations with three cab sizes and two bed sizes in 2WD or 4WD.But it also offers two separate interior concepts unique to GMC.

A six-speed automatic transmission comes standard, a feature only GM can claim.(Only the Dodge Ram diesel offers a six-speed automatic.) The Sierra HD's standard 6.0-liter gas V8 is rated higher than Ford's engine, as is the GMC's 6.6-liter diesel.Also, only GM includes OnStar as standard equipment.

Almost everything you can get in a GMC Yukon sport-utility is available here, including a subwoofer-equipped sound system, navigation, driver memory system, heated leather seats, heated windshield washer fluid, and a moonroof.At the other end of the spectrum, for the entry price of around $24,000 you get a functional pickup with real load-carrying ability and all the safety bits of the top-line model.

The trick in buying a GMC Sierra HD is to give fair consideration and choose wisely.Compute the permutations among three cabs, two weight classes, two beds, two engine/transmission combinations, two drive systems and four trim levels, and then sort out options that cover everything from a diesel radiator cover to rear park assist, and you can see why prices run from that base $24,000 to well past double it.Equip your Sierra HD properly and you'll have an outstanding tow vehicle that offers the comfort and convenience features you want and need.

Trim levels include the commercial-grade Work Truck (WT), the popular SLE, and the premium SLT that resembles a Yukon sport-utility up front.

The base WT model comes with a split vinyl bench seat (and split rear seat on four-door cabs), XM satellite radio, air conditioning, tire pressure monitors, and ABS.

Mid-level SLE models include all basic equipment and add cruise control, chromed steel wheels, electronic shift for 4WD, auto-dimming mirror and compass, driver lumbar, locking seat cushion storage, and leather-wrapped steering wheel.You can add fog lamps and interior upgrades such as cloth-upholstered power-adjustable front seats and redundant controls on the steering wheel.

SLT badges are reserved for the priciest Sierras, those with an interior modeled after GMC luxury utilities.These include as standard leather upholstery with 12-way power and heated front seats, two-person driver memory, heated windshield washer fluid system, locking differential, remote start, towing package, 17-inch aluminum wheels, and a Bose audio system with subwoofer.

The standard gasoline engine for all GMC Sierra HD models is the 6.0-liter V8, which rates 360 hp and 380 lb-ft of torque (322 hp for GVWR above 10,000 pounds).The sole option is a 6.6-liter Duramax turbodiesel, at 365 hp and 660 lb-ft of torque.A six-speed automatic is the only transmission offered.

Options include moonroof, satellite radio, navigation, snow plow prep, integral trailer brake control, remote start, a power takeoff (PTO).Determining exactly the right model and options will take careful and honest shopping because of the sheer number of choices.

Safety equipment includes frontal airbags, front seat belt pretensioners, ABS, and OnStar.Electronic stability control is available on many models.

A new panel forming process gives the dually models integral, seamless rear fender flares and smoother finish for improved paint.This gives the dual rear-wheel trucks a much nicer appearance than that of, say, the heavy-duty Dodge Ram.

The wallpaper sized, ruby red GMC logo makes its origin plainly obvious but the bumper that blends into the fenders gives a much cleaner look and is unusual in HD pickups.Increased frame stiffness allows a smaller gap between the cab and body, and combined with the more aerodynamic windshield and narrower door gaps, makes the Sierra much quieter than its predecessor.

The box sides are deeper by an inch-and-a-bit, the tailgate has a optional lock and assist for closing it with less effort, and the cargo management option fits rails to three sides of the bed; these can be used for tie-down points and to carry a variety of tool or utility boxes.The stoutest Sierra HD's can tow 13,000 pounds with the new 2.5-inch receiver hitch, and the new dual-element mirror and trailer brake control options will lower the stress level.

The Sierra offers similar external dimensions to those of the Ford and Dodge trucks: more than six-and-a-half feet wide outside with room for a 4x8-foot sheet of building material to ride flat in the long bed.

Sierra 4WD versions ride slightly lower than competing pickups, and that inch or two could make the difference in commercial garages or fifth-wheel/bed clearance.The lower bed height is appreciated greatly when loading and unloading cargo.

The high-line Sierra HD SLT features an interior design similar to that of a luxury car or the Yukon Denali.The SLT uses a low-profile dash, a compact instrument cluster, and a center stack with lots of woodgrain trim that rolls off the dash and flows right into a full-length center console.Horizontally oriented vents are positioned at the top, with navigation screen below, and climate controls on the bottom, just above the storage bin that connects to the center console.The SLT dash is sleek, speaks of good fit and finish.Instrument graphics were further upgraded for 2008.The SLT cabin is the nicest, most luxurious, and most comfortable for long-distance towing.

The other Sierra HD models use a more conventional 'pure pickup' layout for the interior, with a higher dash section that goes across the middle and leaves the center open for middle riders, manual-shift transfer case, or communications and safety equipment.The standard dash may not be as stylish as the SLT layout, but it is the more functional of the two and it's equally well assembled.(It received the same improvements when redesigned for 2007 and updated for 2008.) The standard Sierra dash offers more options in small storage, including a second glove box (though with an awkward latch) and a locking storage area with power point beneath the center seat section.There are more places to add accessory switches.Radio and ventilation controls are up higher near line of sight.And the materials produce less glare in low-lying sun and night construction areas.Adjustable pedals and a tilt wheel are available, though the wheel does not telescope and is offset slightly from the seat centerline.

The regular cab has plenty of room for large drivers and space behind the seat for storing a coat and a pair of boots.Extended cabs have articulated side doors that swing 170 degrees for easier loading, the windows in those doors roll down flush, and the seat cushion folds up for more storage.Crew cabs are the obvious choice for anyone hauling more than youngsters on a regular basis, just be sure the middle rider knows there is no headrest.Note that the sunroof shade on high-line versions is literally a shade and not a solid cover, so the interior will warm faster on sunny days.

Operating controls are clearly labeled and logically placed.The shifter offers the typical D and 1 positions, with an M position and thumb tab for individually selecting any intermediate gear.If there's a drawback it is the quantity of similarly shaped and labeled small buttons that butterfingers may have some issues with.Door switches have been revised so your guard dog won't run the window up, but he may still lock you out by stepping on the power lock buttons.Fortunately, OnStar is standard and includes a few months free service; call them and they'll remotely unlock the doors, freeing Fido and your truck.The latest versions of OnStar also offer turn-by-turn navigation, allowing the OnStar operator the option of downloading instructions to your truck that you can then follow on your own.

The fact that the Sierra interior, especially on SLT models, is the most like a car will certainly find favor with those who need a pickup rather than just want one.Apart from turning circle and size, it takes no more to drive this than to drive any other GMC.Life in a Sierra HD is very good, indeed.

The 6.0-liter V8 gas engine has broadly the same horsepower as the old 8-liter big-block, but torque is down roughly 75 lb-ft.Torque is what gets any load moving, up to about 45 mph, and helps keep it moving on grades.On the other hand, the six-speed transmission makes up for a lot, so the absence of a big-block is most noticed in low-range 4WD and the less-forceful shove in your back when you leave a traffic light.The 6.0-liter and six-speed automatic will do about 90 percent of what the big-block 8.1-liter gas engine and four-speed automatic did.And the 6.0-liter will use less gas in the process.The 6.0-liter V8 features an iron block for durability and variable cam timing for efficiency.The 6.0-liter V8 rates 360 hp and 380 lb-ft of torque.It rates 322 hp for GVWR above 10,000 pounds, making the diesel even more attractive for dual-rear-wheel models.

The 6.6-liter turbodiesel option blows the 6-liter gas engine into the weeds for pulling power and fuel economy, though you might say for about $8400 for the powertrain it ought to.Called Duramax, the diesel engine boasts 660 lb-ft of torque available at a much lower engine speed and 365 horsepower.It meets the latest emissions requirements for diesel engines, with reductions of 90 percent in some cases, and the diesel exhaust pipe stays clean and steel-colored inside where the gas engine's pipe is black.The latest generation of induction systems has made the diesel much quieter; your riders may not know it's a diesel if you don't tell them.(The Duramax is approved for B20 biodiesel only in fleet use.)

Pickups of yore tended to buck like broncos on uneven surfaces like turnpike expansion joints, with the bed trying to bounce one direction and the cab the other.Often a function of wheelbase, this can't be completely eliminated in a long vehicle like a Sierra HD, but quality build and engineering does an admirable job of mitigating the motion.

There's heft to the feel of a Sierra, from the way it takes big bumps to the steering and throttle inputs.Its handling characteristics are benign and amount to basic plowing if you push too hard.All-terrain tires give better grip on dirt roads, at the expense of steering precision and noise on tarmac.

Like all big 2WD pickups the Sierra uses all-vented disc brakes with ABS, and independent front suspension.However, only the GM heavy-duty pickups use the same design on 4WD models, giving them a lower nose and more responsive steering.Again, like any big pickup, the tail is prone to kick over impacts with an empty bed; the Sierra is similar to others although it may feel it has more kick because the front is softer.

The optional integrated trailer brake controller will apply your trailer brakes smoother than any aftermarket controller and works in concert with the Sierra's braking system.This controller, however, is not compatible with all brands of electric-hydraulic disc brakes.

The 2.5-inch receiver hitch allows conventional trailer ratings to 13,000 pounds, higher than many competitive offerings; the maximum for fifth-wheels 16,500 pounds.The strongest Sierra HD will haul 23,500 pounds gross combined: the truck, fuel, passengers, cargo, and loaded trailer.

G.R.Whale filed this report to NewCarTestDrive.com from California.