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[2]) the Rounded Line trucks were the first generation of the C/K to be designed with the use of computers and wind tunnels, optimizing the exterior shape for lower drag and improved fuel economy. The chassis was an all-new design (with all trucks receiving a leaf-spring rear suspension); K-Series trucks moved to all-wheel drive (shift-on-the-fly 4×4 was introduced for 1981).