The third generation of the C/K series is a range of trucks that was manufactured by General Motors from the 1973 to 1991 model years. Serving as the replacement for the "Action Line" C/K trucks, GM designated the generation under "Rounded Line" moniker. Again offered as a two-door pickup truck and chassis cab, the Rounded Line trucks marked the introduction of a four-door cab configuration.

Marketed under the Chevrolet and GMC brands, the Rounded Line C/K chassis also served as the basis of GM full-size SUVs, including the Chevrolet/GMC Suburban wagon and the off-road oriented Chevrolet K5 Blazer/GMC Jimmy. The generation also shared body commonality with GM medium-duty commercial trucks.

In early 1987, GM introduced the 1988 fourth-generation C/K to replace the Rounded Line generation, with the company beginning a multi-year transition between the two generations. To eliminate model overlap, the Rounded Line C/K was renamed the R/V series, which remained as a basis for full-size SUVs and heavier-duty pickup trucks. After an 18-year production run (exceeded only in longevity by the Dodge D/W-series/Ram pickup and the Jeep Gladiator/Pickup), the Rounded Line generation was retired after the 1991 model year.

From 1972 to 1991, General Motors produced the Rounded Line C/K (later R/V) series in multiple facilities across the United States and Canada. In South America, the model line was produced in Argentina and Brazil, ending in 1997.

Development Development of the third-generation C/K trucks began in 1968; vehicle components underwent simulated testing on computers before the first prototype pickups were even built for real-world testing. The finished product would become revolutionary in appearance, breaking away from typical American pickup truck design of the era (including the cab). The exterior design underwent scrutiny in the wind tunnel to optimize its aerodynamics and fuel economy. While distinguished by its straight-lined and boxy appearance, GM named the third-generation C/K the "Rounded Line" series, succeeding the "Action Line" C/K trucks.

The largely rectangular front fascia of the Rounded Line trucks (leading to the colloquial "Square-body" and "Box-body" nicknames from the media and publicBrownell, Tom "Rounded-Line Models, 1973–1987" Chevrolet Pickup Color History (Truck Color History) Chapter 9, pp. 88–89 1994-08-07 Retrieved 2011-01-15) led to many departures from previous generations of C/K truck design. As with GM cars, the hood line of the C/K trucks was faired into the front fenders (replacing the clamshell design). While a wraparound windshield (from the Task Force trucks) was never under consideration, a more widely curved windshield (along with curved windshield glass) was added to the cab. To visually integrate the cab with the pickup bed, a shoulder line wrapped from fender to fender around the vehicle (on Fleetside/Wideside beds). Though visually boxier in appearance, the Rounded Line moniker stems from the combination of the wraparound shoulder line and the larger, aerodynamically-shaped windshield.

To further reduce noise, designers removed the mast-style radio antenna, replacing it with a design embedded within the windshield glass. The interior of the C/K trucks underwent major functional changes, replacing the completely flat dashboard with a design closer to its sedans, centering controls and gauges closer to the driver.

Model history Across its 18-year production, the third-generation C/K model line underwent several minor revisions. For 1981, the trucks underwent a mid-cycle revision. To accommodate the 1987 calendar-year introduction of the fourth-generation C/K for the 1988 model year, GM re-designated the third-generation C/K as the R/V series for 1987. Sold alongside its successor as a way to fill in gaps in the model range, the R/V series was produced through the 1991 model year.

1973–1980

For 1973 and 1974, the C/K model line was given a recessed front grille with orange turn signals (GMC grilles were divided in thirds). For 1974, door-mounted drip moldings were added as an option (becoming standard in 1975).

For 1975, the front fascia underwent a minor revision, with Chevrolet replacing the recessed grille with a flush-mounted design (appearing brighter in color); GMC introduced a six-segment grille (splitting the 1973–1974 grille in half). The trim lines underwent a major realignment, as Chevrolet introduced the Scottsdale and Silverado trims. In response to extended-cab Ford and Dodge pickups, a C20 four-door pickup with no rear seat is introduced (dubbed the Bonus Cab), offering additional storage space.

For 1976, engine displacement decals were removed from the grille; a voltage gauge replaced the ammeter in the instrument panel. In another change, the simulated woodgrain exterior trim is discontinued (woodgrain interior trim remains in use for door panels and the dashboard on upper-trim models). The optional wheel covers were revised; a flatter design was introduced for both Chevrolet and GMC with black-painted accents.

For 1977, the front fascia underwent a second revision, with both Chevrolet and GMC receiving larger-segment grille designs. On all trims, the interior received revised door panels (covering a larger portion of the doors). As an option, the C/K offered power windows and power door locks for the first time. The 1978 model year was distinguished by a redesigned fuel-filler door (replacing the exposed fuel cap); woodgrain dash trim (for the Cheyenne and Silverado) was replaced by brushed-aluminum trim.

For 1979, the front fascia underwent a minor facelift. While sharing the same stamping as before, the vertical bars were painted dark gray; chrome trim incorporated the turn signal lenses, giving chrome to nearly the entire front fascia. In line with Fleetside/Wideside trucks, Stepside/Fenderside and Big Dooley trucks replace exposed fuel caps with fuel-tank doors

For 1980, the front fascia underwent an additional update. While GMC trucks carried over the same grille from 1979, Chevrolet trucks received an all-new grille (its first completely new design since 1974). Square headlights made their appearance for the first time on Silverado-trim models; lower-trim vehicles used a combination of the 1980 grille and the 1979 (round) headlight surround.

1981 facelift The Rounded Line trucks underwent a mid-cycle redesign for the 1981 model year. Largely in response to the 1979 energy crisis, GM engineers again turned to wind tunnels to further reduce areas that hindered air flow and caused drag, along with shedding nearly 300 pounds of curb weight from the model line.

While design changes were largely evolutionary (to preserve sales of the highly profitable model line), the body of the C/K trucks was completely reshaped forward of the windshield. While retaining a distinct shoulder line wrapping around the body, the front fenders were reshaped to include a lowered hoodline (relocating the side marker lights); the windshield wipers were now exposed.

As part of the body facelift, the 1981 C/K pickup trucks received new grilles and redesigned front bumpers; Chevrolet grilles were split in the middle by a silver/black bar, with GMC grilles divided into ten squares. Square headlights became standard for the first time; base-trim trucks were fitted with two headlights and upper-trim trucks received four headlights (relocating the turn signal lenses to the front bumper). For the first time since 1975, fender badging was revised, with scripted badging replaced by block lettering (a design that would last through 1987). The interior underwent its own revision, receiving updates to the seats, door panels, and dashboard. The chassis cab option was discontinued on the C10 for 1981.

For 1982, the front fascia underwent a trim revision, with a chrome bumper and a chrome-trim front grille becoming standard equipment. In a functional change, -ton and 1-ton trucks switched from 16.5-inch to 16-inch wheels (to adopt more commercially available tires). To denote the introduction of a 6.2 L diesel V8, vehicles with the diesel engine received specific fender and tailgate badging.

For 1983, the front fascia underwent a minor revision. Along with dropping the two-headlight configuration, Chevrolet and GMC received revised grilles (including the turn signals behind them). For 1984, the two-headlamp configuration returned for base-trim vehicles (relocating the turn signals from the grille to the headlamp surround).

For 1985, the grille was changed for the last time (as the C/K). On two-tone Chevrolet trucks, the center of the grille was painted body-color (in place of silver); for the first time, C/K half-ton trucks were offered with optional cast-aluminum wheels.

R/V-Series (1987–1991)

For 1987, GM began the transition of replacing the Rounded-Line C/K. Though officially sold as 1988 model-year vehicles, the GMT400 generation was launched in April 1987, functionally allowing GM to market two full-size truck lines. The Rounded-Line series was redesignated as the R/V series ("R" = rear-wheel drive; "V" = 4x4) as its successor adopted the C/K moniker; the change was also applied to the vehicle identification number (VIN) of both generations. The 1987 R/V models continued production at Janesville, St. Louis, and Flint; the new 1988 GMT400 trucks entered production December 8, 1986, at Pontiac East, Oshawa, and the new Fort Wayne plant.

For 1988, to shift buyers to the new-generation C/K trucks, regular-cab R/V trucks were discontinued (with the exception of V-series 1-ton trucks and R/V chassis cabs). In a visible exterior change, all R/V-series vehicles received a fender-mounted radio mast antenna, deleting the windshield-integrated unit used since 1973. The R-series -ton pickup became exclusive to Mexico, known as the Chevrolet Cheyenne 2500 (produced through 1991). As part of the nomenclature change, Chevrolet renamed its full-size SUVs, with the Blazer/Jimmy dropping the K5 prefix.

For 1989, R/V-series pickup trucks/SUVs underwent their most visible facelift since 1981. While the front fenders and hood were carried over, the grille was redesigned for a nearly flush appearance (taking on a similar design to its GMT400 successor), with much of the grille trim painted black. Following the trim nomenclature of the GMT400, Chevrolet replaced the Custom Deluxe with the return of the Cheyenne (the Silverado remained in place) while GMC replaced both the standard Sierra and Sierra Classic with the SL and SLE, respectively. In contrast with its successor, both the Chevrolet Scottsdale and GMC High Sierra middle trim levels were eliminated with no direct replacement. Lower-trim R/V trucks were fitted with dual-headlamp grilles while higher-trim vehicles featured quad headlamps. In another major revision, Chevrolet adopted GMC's payload nomenclature, with the R20 and R/V30 being replaced with the R2500 and R/V3500 respectively. In a branding change, GMC dropped the R/V nomenclature externally (though it remained in for the VIN). In another discontinuation, the regular-cab pickup truck was discontinued entirely.

For 1990, the R/V series was pared down further, losing the 2500-series crew cab and the 3500-series regular-cab chassis cab truck. Janesville Assembly produced 3500-series crew cabs (chassis cabs and pickup trucks); Flint Truck Assembly produced the Suburban wagon and K5 Blazer/V-Jimmy. While the Suburban was sold in 1500 and 2500-series, the Blazer/Jimmy was sold only in a 1500 payload series. As a running change during 1990 production, the medium-duty variant of the Rounded Line C/K generation was discontinued, with GM moving its commercial trucks to the GMT530 architecture (replacing the C50-C70/7000, Chevrolet Kodiak/GMC TopKick, and the GMC Brigadier under a single product range).