The #1 culprit for this is a monitor that is set too bright.  Calibration doesn't address that.  The best thing to do is to print a standard test image on standard paper.  I don't see any metallic glossy papers listed in the P900 driver and a lot can happen when using/adding new media types so it is best to start with a standard test on a common paper like standard Epson Glossy.  See if you have the same problem with that.  If so, it's likely your monitor is too bright which is causing you to edit or accept photos too dark (which is how they print).

Regards,
Mike