What was the first year for the "Z71" option on a 3/4 ton?

[jocko]

And by Z71 option, I mean the GMT400 era trucks like these with the Z71 sticker on the side of the truck. I'll be honest, I used to think this was a 1/2 ton-only option, but I've noticed some of the newer trucks (as in, very new 3/4 tons) with the Z71 sticker. Just curious what year the option was first available on a 3/4 ton and when the sticker was first seen on a 3/4 ton. Thanks!