I'm pretty sure its the 5 X 5" pattern. I'm pretty sure that's the standard from '71-'98 for the half-ton trucks with the 5 bolt pattern.
That's what I have on my 79, and that was what was on my '83 when I had it. When I look at the chevy rally wheels on ebay they also say the same thing.
5 X 4 3/4" was mainly used on passenger cars and S-10s.