The first full-size pickup truck was the Chevrolet C/K, which was introduced in 1960. The C/K series was a full-size pickup truck that ranged from light-duty to heavy-duty.
It was available in two-wheel and four-wheel drive configurations. The original design featured a straight body style with a boxy design, and it had a wide range of engine options ranging from a small inline four-cylinder to a large V8 engine. The C/K series also featured an independent suspension system which allowed for better handling and ride comfort compared to other trucks of the era.
The Chevrolet C/K series was an immediate success and it paved the way for other full-size pickups like the Ford F-Series and Dodge Ram. While the basic design of the C/K remained relatively unchanged for over three decades, there were several updates made throughout its lifespan including changes in body style, powertrain options, suspension systems, and interior features. The last generation of the C/K Series was produced in 1998 before being replaced by the GMT400 platform which formed the basis for modern pickup trucks like the Chevrolet Silverado and GMC Sierra.
Conclusion: The Chevrolet C/K Series is considered to be the first full size pickup truck ever produced. It set the stage for all other full size pickups that followed and its design has seen many updates over its long lifespan, making it one of the most successful pickup trucks ever produced.