Knuckle Buster

An all-new clean sheet redesign of General Motors' Chevrolet and GMC brand C/K-Series pickups débuted in mid-1972 for the 1973 model year. Development of the new third-generation trucks began in 1968 with vehicle components undergoing simulated testing on computers before the first prototype pickups were even built for real world testing. The redesign was revolutionary in appearance at the time, particularly the cab, departing from typical American pickup truck designs of the era. Aside from being near twins, the Chevrolet and GMC pickups looked like nothing else on the road. The third-generation trucks are colloquially known as the "Square-body" or "Box-body" generation. GM's official "Rounded-Line" moniker highlighted the pickup's rounded styling cues that were incorporated into the design. This included rounded windshield corners, rounded corners of the cab roof, rounded-corner doors which cut high into the cab roof eliminating roof height, slanted front fenders, and rounded pickup box corners which allowed for rounded wraparound taillamps, a first for GM pickups. The design also featured strong distinctive curved shoulderlines which rounded out below the beltline. The curved shoulderline continued across the back tailgate on Chevrolet Fleetside and GMC Wideside models. However, the low slope of the hood and rectangular front end of the truck originated the "square/box-body" nickname, which was propagated through truck magazines and word of mouth.

A new Eaton Automatic Differential Lock (ADL) was introduced in 1973 as an optional extra on the Rounded-Line C/K-Series pickups, for the rear hypoid differential.