The GMC was the low end of Chevrolet and were mostly work or farm trucks. They didn't get all the frilles as the Chevrolet.
That's why GMC had more chrome and offered an automatic transmission two years BEFORE Chevrolet.
Can you name even one frill that was standard or optional on a Chevrolet that was not also standard or optional on a GMC?
GMC was positioned back then as the Buick or Oldsmobile against the plainer Chevrolet, as the nicer better equiped truck with the bigger more durable motor.
You've got the relationship between the two brands exactly backwards.
