Was the Silverado always its own model?
Quick Answer
No. For the classic era, Silverado was the top trim level on the Chevrolet C/K pickup, from 1975 onward, above Scottsdale and Cheyenne. It only became a standalone model name in 1999. So a classic "Silverado" is really a loaded C/K truck.
The name has two lives.
As a trim (1975-1998)
Silverado was the dressiest C/K package, with the woodgrain dash, full gauges, and brightwork. The trucks collectors chase, the square-body and the OBS, wear it as a trim.
As a model (1999+)
Only in 1999 did Silverado become the name of the truck itself, after the classic era.