GMC introduced the third and final generation of GMC C/K for the 1973 model year. The GMC C/K was an upmarket version of the Chevrolet C/K, and was offered in light, medium, and heavy duty variants. This new generation featured redesigned styling, leading to the third generation being commonly referred to as 'square body'. A wide range of V8 engines were available, as well as a few inline six, and one V6 option. As with previous C/K models, rear wheel drive variants were designated 'C,' while four wheel drive variants were designated 'K.' Starting in 1975, three trim levels were offered: Sierra, Sierra Grande, and High Sierra. For 1987, in anticipation of the next generation, rear wheel drive variants were designated with an 'R', while four wheel drive was designated with a 'V'. As GMC transitioned to the GMC Sierra, 1500 variants were last built in 1987, 2500 variants were last built in 1989, and 3500 variants lasted until 1991.