Ditto on checking for rust.
I thought the option sheet was on the glovebox door? I recall several years ago having the itch to get a Silverado, and was looking used, and there was a website where, once I registered, I could have up to 5 VIN's decoded. Chevy models of course, but it'd tell what diff gearing etc. No idea if still around. But perhaps the local dealership could decode it for you?