Fuel standards changed in 1976 with the introduction of unleaded fuel. I believe it was two years later that GM Trucks were required to use unleaded fuel. I had a 78 and it used unleaded only. DrMike
They didn't change over all at once. It depended on GVW. If I remember correctly,1/2 tons went unleaded a couple of years before the 3/4 and 1 tons.
