If you're still having trouble with printing on both sides, try this:
Devices and Printers, Right-click the P2055dn icon, printer properties, device settings tab. Scroll down to Duplex Unit. If it is set to Not Installed, click on the phrase Not Installed and select Installed from the drop down menu. Press OK. Then, after
you select print for a specific job, select properties and change Print on both sides from No to Yes, flip over or to Yes Flip up. Most users know to do this last step, but the choice is only there if you've set the Duplex Unit to Installed. I got this solution
from a post in another forum. Good luck.
I'm still among those who can't get the tool box and am getting the GET DevMgmt error, but I can print duplex!!