4 Of GMC's Most Iconic Square Body Trucks

In the world of old body style pickup trucks, it's often difficult to find people that agree on much; however, most will agree that square-body trucks are some of the best-looking designs ever produced. The term square body, of course, describes the truck's boxy exterior, a feature many find quite endearing. While Chevrolet is the car brand most closely associated with square-body trucks, GMC put its brand on some iconic square-body trucks as well.

Historically, there isn't a lot of difference between Chevrolet and GMC pickups. Mechanically, they use nearly identical drivetrains, suspension components, and sheet metal. Notable differences often lie in the grille and headlight assemblies, interior finishes, and tech features, with the GMC typically featuring slightly more upscale components.

One of the most successful models in GM's history, Chevrolet and GMC produced square-body pickup trucks from 1973 to 1987 (or 1991 for heavy-duty models), a period that encompassed the C/K trucks' third generation. With the two GM divisions producing square-body trucks for 15 model years, they aren't necessarily rare, but their popularity to date often makes them worth more today than when they rolled off the assembly line, even when adjusted for inflation.

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In step with its corporate partner Chevrolet, GMC rolled out its first square-body trucks for the 1973 model year with the launch of the third-generation C/K-series pickup trucks. The previous generation trucks, known as the Action Line, saw General Motors take steps to transition its pickups from the workforce to a broader consumer base by making them more comfortable. While this was especially true for half-ton models, the theme carried over to heavy-duty models as well.

The trend continued into the third generation, a line that GM officially referred to as the Rounded Line as the company had spent considerable effort on producing a truck with improved aerodynamics. However, pickup truck enthusiasts didn't embrace the name, as there was little about the exterior of the truck that appeared rounded, so the square-body name stuck and persisted, seemingly for all time.

As a continuation of the C/K-series, C-series trucks were rear-wheel drive, while the K-series denoted four-wheel drive models. Also, C/K10 indicated half-ton nominal payload, whereas C/K20 and C/K30 trucks had three-quarter and one-ton payload capacities. Trim levels included the base Custom, Super Custom, Sierra, and range-topping Sierra Grande.

In 1973, a half-ton GMC Sierra square-body truck cost about $2,900 MSRP, $21,618 when adjusted for inflation. Today, average retail is estimated at nearly $27K, and the most recent 1973 GMC Sierra Grande sale recorded by Classic.com went for $31,000.

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The first GMC square-body truck grilles featured three recessed rectangular blocks framed by a pair of round headlights. For 1975, GMC introduced a new look for the front of its C/K pickups by adding a horizontal bar across the three-panel grille to create a six-segment look. While the round headlights remained unchanged, other subtle tweaks included a switch from orange turn signal lenses to an opaque white.

The 1975 model year also saw adjustments to the GMC C/K-series trim levels. Sierra became the base trim and Sierra Grande was demoted to the second level. The new High Sierra trim was near the top level just below the Sierra Classic at the pinnacle. These trim designations would stay in place for the remainder of the generation. It was also the first year of the "heavy-half-ton" models, designated with C/K15 rather than the traditional C/K10.

Original MSRP climbed to around $3,600 for 1975 (about $21,120 in 2024 dollars); however, 1975 GMC square-body sales over the last five years averaged $25,075 according to Classic.com. The top sale for the period raked in $33K, but the most recent only went for $9,500.

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While the decals indicating which engine was under the hood were removed from the grille in 1976, the 1977 square-body GMC trucks received an all-new grille design. The horizontal bar remained to split the grille into top and bottom halves, but the three recessed panels from the original design became five to create 10 blocks with a squarer shape. Other front fascia features remained as well, such as the opaque turn signal lenses, dual round headlights, and vertical side markers.

Upscale touches, such as power windows and power door locks were added to the list of available options. In addition, larger padded door panels reduced the hard metal surface area inside the cab.

The new K30 was introduced for 1977, adding the one-ton chassis to the four-wheel drive lineup. The K-series GMCs also began using the Dana 60 front axle for the first time.

A 1977 GMC Sierra C15 carried an MSRP of around $4,120 (close to $21,500 when adjusted for inflation). J.D. Power estimates an average retail value of $31,400, however, Classic.com reports an average value of $25,208 spread over 22 sales in the last five years. The top sale for the period went for $60,500 and the most recent sold for $8,800.

In preparation for the 1981 model year, GM designers headed back to the wind tunnel to fine-tune the square body's aerodynamics. The result was a lowered swept-back hood line with some additional cosmetic alterations. While the grille retained the 10-panel look of previous years, the inner fins came forward to brighten its appearance. A pair of square headlights replaced the single round light on each side on some trims, while a single square headlight per side was used on lower trims. Additional changes to the C/K-series front end included moving the turn signals to cutouts in the front bumper and rotating the front side marker lights from vertical to horizontal.

GM also adopted a four-digit model designation for its C/K trucks; for example, what was a 15 changed to a 1500. More substantial changes included a new aluminum two-speed transfer case and optional automatic self-locking hubs on K-series trucks. The automatic hubs removed the requirement to exit the truck to lock in four-wheel drive and the dual-range transfer case allowed shifting into four-wheel drive while on the move. It also allowed the truck to operate in two-wheel drive mode when driving on dry roads, or selecting between high- and low-range 4x4 options.

By 1981 the MSRP for GMC square-body trucks had risen to $6,000 ($20,835 in 2024 dollars). J.D. Power reports average retail prices today at $25,900. However, the most recent sale recorded by Classic.com brought $52,800 at a Barrett-Jackson auction in April of 2024.

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