first generation would not undergo a comprehensive facelift or update, GM would make a series of gradual changes to the model line through its production. For 1962, the hood was redesigned, with a new windshield and A-pillar added to the cab for 1964. In a break from General Motors tradition, this is one of the few generations of trucks not given an in-house moniker. The C/K nomenclature was developed by GMC; "C" denoted conventional cab, with "K" standing for 4x4 drive. Second generation (1967–1972) The second-generation C/K was introduced for the 1967 model year. Designated the "Action Line" generation by General Motors, the C/K largely carried over its drop-center ladder frame and its coil-sprung rear axle, but the body was redesigned from the ground up to improve its capability as a multi-purpose vehicle. Alongside a utilitarian vehicle intended for work or farm use, the C/K was also offered with optional features carried over from Chevrolet sedans, including automatic transmissions, AM/FM radio, carpet, and two-tone paint. While the Action Line would not undergo a definitive model revision through its production, the series underwent gradual changes on a biannual basis. The drivetrain line underwent multiple revisions, as a large-block V8 was offered for the first time in 1968. After 1969, GM switched entirely to Chevrolet-produced engines for C/K pickup trucks. This generation marks the debut of the Chevrolet Cheyenne and GMC Sierra nameplates; introduced in 1971 and 1972, respectively, General Motors still uses both nameplates for full-size pickups in current production. The Action-Line pickup also served as the basis of ancestors of modern full-size SUVs, including the Chevrolet K5 Blazer, an open-body off-road vehicle, and the Chevrolet Suburban truck-based station wagon. For 1973, GM replaced the Action Line trucks with the long-running Rounded Line series; the Action Line trucks are the final C/K trucks offered solely with a two-door cab. Third generation (1973–1991) The third-generation C/K was introduced for the 1973 model year. Designated the "Rounded Line" generation by General Motors, the C/K grew in size inside and out. As pickup trucks increased in use as personal vehicles, cab features and options moved closer in line with GM sedans (with power windows and power door locks becoming options). To further expand its practicality, a four-door crew cab body was introduced (offering 6-passenger seating). While relatively straight-lined and boxy in appearance (leading to their "Square-body" nickname from the public) the Rounded Line trucks