Interesting. Yeah, that seems like flex fuel label. Are you the original owner of this truck?
Can you post a photo of the injectors? The L59 are visually different than those from the non flex-fuel variants.
Things get swapped over the years and ownership. Possibly engine, glovebox or fuel door are not original?
For example:
On my 99 Silverado I swapped the engine from a V6 to an L59, transmission from a 4L60e to a 4L80e, and last year I deleted to center console to a jumpseat (including the glovebox with another truck's RPO code label.) I did keep my old glovebox, and I was going to swap the lid, but even then, stuff doesn't match exactly. LoL