It is possible you may have added the printer into the print and scan with an Airprint driver rather then the Officejet driver. If you click on the Apple icon then select System Prefrence and open Print and Scan. In Print and Scan click on the printer on the left and click the minus symbol below this will delete the printer. Click the plus symbol and choose add another printer or scanner, you will then see your printer and select it, but below you will see "print using" and by default it will likely say "airprint" click on airprint and choose the Officejet driver that appears.
Try printing again and see if it makes a difference.
Hope this helps,
I work on behalf of HP.
Thanks for the suggestion. Unfortunately when I added the printer there was nothing on the screen that referred to "print using" and no reference to AirPrint. Do I have an older version of the 7410 and that's the reason? Whatever, I'll try to print docs and see if the speed is back to normal. If you have another suggestion let me know.