It very well may be, that you need a new printhead.. You can get a new printhead here, but they are tough to remove and install.
While that is most likely what needs to be done, we should try a few other things as well.
First, have you tried resetting the printing system on your mac and reinstalling the printer. Here is how to reset the printing system
Choose System Preferences from the Apple menu.
Click Printers & Scanners.
In some versions of OS X, this preference is named Print & Scan or Print & Fax.
Control-click anywhere in the list of devices on the left, then choose “Reset printing system” from the shortcut menu that appears.
Then, we need to reinstall the printer using the correct and newest driver from this page.
Once you have reinstalled the printer driver from that page, test print again.
if it still doesnt print correctly, there is one last thing we can try.. But I need you to respond after the above has completed and let me know the results of each step, and we will go from there.
I strive to provide great service, and greatly appreciate a 5 star rating clicked and submitted when you are satisfied.. I always answer follow up questions.
Senior Technician and Network Switching Systems Operator / Maintainer.