Just found this link, Comprehensive Chevrolet, Saturn, GMC, Hummer, Cadillac, Buick, Oldsmobile, Pontiac, Geo, Dodge, Plymouth, Jeep, Chrysler, Ford, Lincoln, Mercury, Mazda Truck, Mercedes VIN Decoder
Lists all RPO for your can with VIN. GM dealers use internal database.
Was helpful since I bought my car used and didn't know exactly what was in the car when it left the build plant.