For 2006, there's an all-new, more powerful version of Chevrolet's 'Duramax 6600' 6.6-litre V8 turbodiesel: the engine now makes 360 hp at 3200 rpm, and 650 lb-ft of torque at 1600 rpm. It's an option on the Silverado 2500HD and 3500HD (heavy-duty), in all cab configurations (regular, extended and crew), and in six-foot-six or eight-foot box. Despite its extra power, the new engine produces fewer emissions than its predecessor, and it's quieter. My four-wheel-drive 2500HD was also equipped with an optional, all-new six-speed Allison 1000 transmission, which replaces the five-speed Allison of 2005. GM says the 6-speed Allison transmission is the first in its class, and it can be added to the Duramax 6600 diesel or the Vortec 8100 8.1-litre V8 gasoline engine.

Among the engine changes GM lists are modifications to the cylinder block casting and machining process which strengthens the bottom of the cylinder bores; upgraded main bearing material; lower compression ratio (16.8:1, from 17.5:1); larger piston pins and connecting rod sections; a higher-pressure fuel pump and seven-hole injectors that spray directly onto the glow plugs; a new intake air heater to reduce smoke and emissions during cold or light-load driving and to speed engine heating; and a retuned air induction system to reduce noise.

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The variable-geometry turbocharger has also undergone some modifications; it spins at up to 120,000 rpm and improves the engine's overall smoothness. As well, it can provide exhaust braking. Offered as an optional factory-installed feature, the driver-activated brake replaces an aftermarket exhaust brake system.

Chevrolet's best-selling truck undergoes only a few trim changes for 2006, including a revised grille design and a "power dome" hood, previously found only on the 3500 models. (The number designations, by the way, indicate cargo capacity: 1500 is a half-ton, 2500 a three-quarter-ton, and 3500 a one-ton.) I still think Ford and Dodge trucks are better-looking, but taste is subjective, of course, and the Silverado's front-end design is clean if not memorable.

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Climbing up into the cab - and it's quite a way up, even with optional side steps - I slid onto thick and very comfortable leather-clad heated seats, which are included in the top-of-the-line LT package (you can also get Base or mid-range LS). The trim line also includes eight-way power adjusters for driver and passenger, dual-zone electronic climate control, six-disc CD changer with wheel-mounted controls, and power folding mirrors with integrated turn signals. The dash doesn't change much between trim lines, though, and so you're looking at a very plastic-heavy panel while sitting on a very wide expanse of cowhide. It's a very practical dash for a work truck, but it doesn't look in line with the luxury price-tag, which hit $61,885 on my tester.

Much of that money goes into the powertrain: the Duramax diesel is $7,300, the six-speed transmission $1,545. That, plus the sheer size and power, means that very few of these will end up solely as "big car" pleasure vehicles. That's not the intent. This is a truck meant to run all day, doing serious work; it can carry 1,435 kg (3,163 lbs), tow a ball-hitched trailer up to 5,443 kg (12,000 lbs) and manage a fifth-wheel trailer up to 6,623 kg (14,600 lbs).

An improved starting system reduces glow plug warm-up considerably; it only takes a few seconds, and if the engine's warm, the dash warning light doesn't come on at all. There's still considerably more engine noise than with gasoline, of course, but it is quieter than might be expected given its size and power.

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The six-speed transmission uses a column shifter that includes both tow/haul mode and a tap-down shift feature. The tow/haul mode doesn't just lock out overdrive, but triggers a more aggressive shift pattern. Pull the shifter down a notch into "Manual", and by flicking a toggle switch on the shifter, you can control the shifts as you would with the auto-shift function on a car transmission.

The four-wheel drive system operates via dash-mounted buttons, and all but 4Lo can be shifted at any speed.

As is to be expected, the ride on this heavy-duty hauler is choppy when it's empty, but there's very little road noise; for what it is, this is a very quiet truck. Heavy-duty models feature an independent front suspension with extra-strong control arms and torsion bars. Steering is relatively light but accurate, and the brakes are good and solid. Acceleration is strong, and it runs through its six gears fairly quickly. I averaged 18.4 L/100 km (15 mpg Imp), but that should improve considerably, since at only 700 km the big diesel was barely broken in (due to the truck's size, official government fuel economy figures are not available).

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In the LT trim line, front passengers are divided by a wide central console, with cupholders and storage. There are three cubbies in the centre stack, but they're shallow and uncovered, so don't pack them too full. The pricey sunroof - $1,480, which bundles it with the garage door opener - comes with a mesh cover that stays locked until it's manually opened, which means you can open the glass for ventilation but keep the mesh closed to cut the glare.

The cluster contains full instrumentation, and the information centre in the speedometer includes an engine hour meter, which logs the number of hours the engine has been in use.

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Rear-seat passengers in the crew cab enjoy considerable leg room and four cupholders (two in the back of the console, two in the pull-down armrest). The rear 60/40 seat can be folded by flipping the cushion up and dropping the seatback down, to provide a flat cargo floor that really should be plastic - or rubber-covered instead of carpeted.

• Buyer's Guide: 2006 Ford F-Series
• Buyer's Guide: 2006 Dodge Ram