Specifications of a Medium-Duty GMC Truck

by Rob WagnerUpdated July 05, 2023

The GMC C-Series TopKick truck and its sister trucks, the Chevrolet Kodiak and the Isuzu H-Series, are medium-duty commercial vehicles employed as cargo haulers, work vehicles and dump trucks. The medium-duty GMC trucks are equipped with gasoline and diesel engines for maximum towing capacity. The Ford F-650 and Dodge Ram 6500 are competitors.


General Motors began production of the GMC medium-duty C-Series Topkick in 1980. Initially identified as the C-Series, GMC officially took on the TopKick moniker when the second generation of trucks was launched in 1990. The Chevrolet version took on the “Kodiak” nameplate. Financially troubled GM announced in 2007 that it planned to sell its medium-duty truck line. But GM couldn’t find a buyer, and the GMC TopKick and Chevrolet Kodiak ceased production in 2009. Models were still sold in 2010, according to MSNBC.

The TopKick

The medium-duty GMC TopKick is formally identified as the C4500 Series with a gross vehicle weight rating ranging from 16,500 to 63,000 lbs. Seven models were offered in regular and crew-cab configurations. Models featured two- and four-wheel-drive. The trucks are primarily used in regional hauling operations, such as carrying cargo from one city to another, or for workhouse duty at construction sites employed as dump trucks or water trucks. They are also used as flatbed haulers and tow trucks.


The 2009 medium-duty TopKick features a state-of-the-art comfortable interior with driver- and passenger-side airbags, air-suspension bucket seats, a curved instrument panel for easy navigation, underseat storage and two 12-volt AC power outlets. A special feature was an automatic shutdown system for the engine to prevent damage if the engine suddenly lost oil pressure or experienced another malfunction.

Under the Hood

The 2009 medium-duty GMC could be equipped with one of three engines: the gasoline-powered 325-horsepower Vortec 8.1-liter V-8, the 300-horsepower Duramax 6.6-liter diesel V-8 and the Duramax 6.6-liter diesel generating 330 horsepower. The 330-horsepower diesel is perhaps the most popular of the three engine selections. It’s supercharged by IHI Turbo America. It features a 4-inch bore, 3.89-inch stroke and a 17.5:1 compression ratio. The engine wields 620 foot-pounds of torque, the twisting energy generated inside the engine to give the truck its hauling capacity. Power is transmitted via a six-speed Allison manual transmission.

Bore Definition

The bore is the inner diameter of a cylinder in an engine.

Size and Capacity

The 2009 medium-duty TopKick was offered in a 170- or 176-inch wheelbase and measured 265 inches long, 95.9 inches wide and 95.2 inches tall. Average curbside weight depending on the model was 11,300 lbs.


The 300-horsepower Duramax diesel TopKick, which generated 520 foot-pounds of torque, could achieve 0 to 60 mph in 14.4 seconds and the quarter-mile in 19.8 seconds at 68 mph. Gas mileage was about 8 miles per gallon. Payload capacity was 5,000 lbs. and towing capacity was 14,300 lbs.

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