Welcome to the Stovebolt, 455lark.
I had a 50 pickup back in the mid seventies and currently a 52 panel but never seen a number like that. Maybe a service truck for a plumbing or heat and air company.....and who knows, they may have started the numbers at 2000???
Your truck stock, modified in some way? Whats your future plans?
Are you close to Phoenix ? I know a bolter there by the name of Al.