Duplex Printing for HP Color LaserJet CP4005dn Setup

How can I get my duplex printing to show up/work from the printer pop-up menu. Have installed all HP CP4005dn drivers. Installed the printer with all installable options. Printer works fine except no duplex print options. Have followed Mac Help's "Displaying a printer's special features when you print" to the letter. Nada. Have UNinstalled the printer. Downloaded all Mac updates. Downloaded all HP updates. Have reinstalled the CP4005 printer with intallable options. Still no duplex print options. Where is the miss? Why can't I get the duplex to function?