The fourth generation of the C/K series is a range of trucks that was manufactured by General Motors from the 1988 to the 2002 model years. The successor to the "Rounded Line" generation of C/K trucks, the fourth generation was given the GMT400 platform codename. Marketed by both Chevrolet and GMC, the fourth-generation C/K was offered as both a pickup truck and chassis cab-vehicle. Alongside two-door and four-door cabs, a two-door extended cab was released for the first time.

In a branding change, the C/K nomenclature became exclusive to Chevrolet, as GMC adopted the GMC Sierra nameplate for all its full-size pickup trucks. The GMT400 platform retained tradition with its predecessors, again serving as the basis of GM medium-duty commercial trucks (the Chevrolet Kodiak/GMC TopKick) and for full-size GM sport-utility vehicles (the Chevrolet/GMC Suburban and the Chevrolet K5 Blazer/Tahoe, GMC Yukon, GMC Yukon Denali, and Cadillac Escalade). After its production, the GMT400 generation became informally known as "OBS" (Old Body Style) trucks), in reference to its GMT800 successor. In starting a different tradition, the model line overlapped production with both its predecessor and successor.

Over nearly a 14-year production run, the fourth-generation C/K was assembled by GM in multiple facilities in the United States, Canada, and Mexico. After the 2000 model year, the fourth-generation C/K was discontinued and was replaced by the GMT800 platform (introduced for 1999); the C3500HD heavy-duty chassis cab model remained in production through 2002 for the US market and up to 2006 for the Mexican market.

Following this generation, Chevrolet subsequently retired the external C/K branding; in line with GMC's Sierra nameplate, the single Chevrolet Silverado nameplate has been used for the full-size truck line since.

Development The development of the fourth-generation C/K began in the early 1980s with design operations headed by General Motors Truck and Bus Group. Computers took on a greater role to develop the model line as GM used computer data to develop both components and tooling for the vehicle. Key objectives included reducing weight (in the interest of improving fuel economy), improving aerodynamics and handling, and upgrading interior comfort. The second model family to adapt the GMT platform nomenclature, the fourth-generation C/K ended the tradition of GM monikers for full-size trucks (i.e., Rounded Line, Action Line, Task Force, Advance Design), taking on the GMT400 internal codename.

Styled with straighter lines than its predecessor (to maximize interior space and improve functionality), the exterior of the GMT400 was designed to optimize aerodynamics (to further increase fuel economy). Fitted with a flush, curved grille and front bumper, the body was designed with sedan-style doors with flush window glass. GM debuted an extended-cab configuration for the C/K line about 15 years after its introduction by Dodge and then Ford. GM also removed vent windows from the C/K trucks (the first full-size truck line to do so), nearly 20 years after removing them from its car lines.

K-Series four-wheel drive trucks underwent multiple functional upgrades. The solid front axle was replaced by independent front suspension (closer in configuration to C-Series trucks); operation of the transfer case was simplified with the standardization of a shift-on-the-fly system. To enhance durability, the chassis was redesigned with a fully welded frame with a boxed front section for strength and rigidity; to better resist corrosion, additional galvanized steel was added to the body.

R/V series (1987–1991) For the 1987 model year, GM redesignated the Rounded-Line Series C/K trucks as the R/V series (R = rear-wheel drive; V = 4×4). The nomenclature change was done to accommodate the launch of the GMT400 C/K; though launched for the 1988 model year, the newer product line went on sale in April 1987. In a more subtle change, the R/V trim levels were revised (to match the GMT400 C/K).

For the traditional autumn launch of the 1988 model year, GM began to transition buyers further into the new model line, withdrawing -ton R/V trucks (-ton trucks were discontinued after 1988). For 1990 and 1991, the R/V series consisted of 3500-series crew-cab pickups and chassis cabs, which also served as the basis of the Suburban and Blazer/Jimmy full-size SUVs.

For 1992, crew cabs/chassis cabs (and full-size SUVs) moved to the GMT400 chassis, marking the end of the Rounded-Line series after 18 model years.

Model history The fourth-generation GMT400 C/K model line was introduced in April 1987 for the 1988 model year. Produced for nearly 14 years, the fourth-generation C/K underwent multiple minor revisions through its production, including a mid-cycle revision for the 1995 model year.

From 1988 to 1991, the model line was sold alongside its predecessor (the "Rounded-Line" C/K) and was sold alongside its successor (the GMT800 Silverado/Sierra) from 1999 to 2000. Thereafter, pickup trucks were discontinued, with the model line sold only as a C3500HD heavy-duty chassis cab through 2002.

1988–1994 For 1988, the fourth-generation C/K was introduced, including (nominal) -ton, -ton, and 1-ton pickup trucks and chassis cabs. In a nomenclature revision, the 1500/2500/3500 payload series previously used by GMC was also adopted by Chevrolet (the Rounded-Line R/V series would do so for 1989). At its launch, the new generation was offered in three cab configurations and two bed configurations; the extended cab was a first for GM full-size trucks.

For 1990, Chevrolet and GMC pickup trucks underwent a minor exterior revision, with upper trims (Chevrolet Scottsdale/Silverado, and GMC SLX/SLE) replacing four sealed-beam headlamps with white-lens composite headlamps; base trims (Cheyenne and GMC SL) continued the use of two sealed-beam headlamps. Two new versions (exclusive to Chevrolet) were introduced: the W/T 1500 and the 454SS. The W/T 1500 (W/T stands for Work Truck) was a de-contented version of the Cheyenne marketed primarily for work use and was only available with the 4.3L V6, regular cab, and 8' bed (a 6.5' Fleetside bed was later available); the 454SS combined elements of the Sport Equipment Package with the 7.4L V8 of 3500-series trucks.

For the 1992 model year, the Rounded Line (R/V series) was retired (after 18 years), with GM moving the crew-cab pickups and full-size SUVs to the GMT400 model line (nearly five years after its introduction). The single-seat "Bonus Cab," which was a crew cab without the rear seat, was not carried over as its design had effectively been overtaken by that of the extended cab. In another change, trim levels were reduced to two, with the mid-level Chevrolet Scottsdale and GMC SLX withdrawn.

For 1993, the body of the GMT400 saw few changes, introducing front bucket seats for extended-cab pickups.

For 1994, both low and high series grilles were refreshed and a combination center high mount stop lamp and cargo light (A standalone cargo light was previously optional.) was added above the rear window to comply with a new federal requirement but the rest of the body was carryover. There were also several mechanical changes: the 4.3L V6 was no longer available on extended-cab models with 8' bed, 2500-series extended cabs, or on heavy-duty 2500 series models, and the light-duty 2500 extended-cab with 8' bed was discontinued.

1995–1998 For the 1995 model year, all GMT400 trucks underwent a mid-cycle revision. The dashboard, door panels and seats (as well as the front center console on bucket seat equipped models) were completely redesigned. The sideview mirrors were redesigned and enlarged (adopted from the Suburban SUV); on extended cabs, opening rear side windows became standard equipment. Several updates coincided with safety mandates, adding a driver-side airbag to all models with a GVWR under 8,500 pounds (including all 1500 models and some 2500 models), four-wheel ABS, and a brake-shift interlock for the transmission.

For 1996, as a running change through the model year, extended-cab models were available with a passenger-side third door. Introduced at nearly the same time as Ford (though a model year before), the feature was an option for 1500-series extended-cab short-bed trucks with 5.0L or 5.7L V8 engines and automatic transmissions. The bench seat of Silverado/SLE-trim vehicles underwent a revision, with the center seatback converted to a fold-down armrest/console. In another change, the GMT400 platform, as with all other GM vehicles, received daytime running lights as standard equipment. Also, the 2500 could no longer be had with the 4.3L V6 engine and the light-duty 2500 4×4 trucks were discontinued.

For 1997, the dashboard underwent a minor revision to accommodate a passenger-side airbag (only vehicles with a GVWR under 8,500 pounds were equipped, including the 1500 series and light-duty 2500 series).

For 1998, GM revised the tailgate badging for pickup trucks. To reflect the 1996 divisional merger of GMC and Pontiac, "GMC Truck" became "GMC" on all Sierras; Chevrolet introduced a tailgate badge for Silverado-trim pickups which is similar in appearance to that found on the Suburban and Tahoe SUVs.

1999–2002 In August 1998, General Motors released the GMT800 generation of full-size pickups for the 1999 model year as the replacement for the fourth-generation C/K trucks introduced for 1988. The long-running C/K nomenclature was retired by Chevrolet in favor of a singular Chevrolet Silverado nameplate (as GMC had done in 1988 with the GMC Sierra).

For the 1999 model year, GM continued sales of the fourth-generation C/K alongside its GMT800 successor, intending to use up leftover parts stock. The Chevrolet C/K and the newly-rebranded GMC Sierra Classic were largely aimed towards fleet sales and were still offered in all three payload series. To minimize production costs, the 1500-series C/K and Sierra Classic were offered only with the three-door extended-cab/6.5' Fleetside bed configuration, and with the 5.0L or 5.7L V8 engine paired to an automatic transmission, and the light-duty (under 8,500 pounds GVWR) 2500 series was discontinued. It also offered much of the previous Silverado interior trim. The changes for 1999 were an effort to steer potential base-trim or W/T 1500 buyers toward the all-new Silverado.

Also, in the fall of 1998, GM introduced the C/K crew cab with the 6.5' bed. It was available in the 2500 or 3500 series and two- or four-wheel drive. The 2500 series was available with the 5.7L or 7.4L V8 gasoline engine, or the 6.5L V8 diesel engine, and came with a GVWR of 8,600 pounds. The 3500 series came standard with dual rear wheels (the only short-bed GM pickup to have such a feature), a 7.4L V8 (or a 6.5L V8 diesel), and a 9,400 pound GVWR.

For 2000, the C/K and Sierra Classic were pared down to the 2500 and 3500 series (above 8,500 pounds GVWR), with the model line reduced solely to the C3500HD chassis cab for 2001 and 2002.

Model overview The fourth-generation C/K pickup trucks were marketed by the Chevrolet and GMC divisions of General Motors. Offered in 1500 (1⁄2-ton), 2500 (3⁄4-ton), and 3500 (1-ton) payload series, the C/K pickup trucks were sold in two-door standard cab, two- or three-door extended cab, and four-door crew cab configurations. In total, six wheelbases for pickup trucks were offered. The C/K product line also included General Motors full-size SUVs (again derived from the body of the crew cab).

Chassis

While again using the perimeter-frame layout of the Rounded-Line C/K trucks, the fourth-generation chassis was an all-new design, adopting fully-boxed frame rails forward of the cab. In a first for the model line, power steering became standard on all C/K trucks for 1988. For 1997, the system was revised to a variable-ratio assist system.