Hello mshack,
Welcome to the HP Forums! I understand your concerns with your Photosmart 7520. How is this printer connected? Wireless or USB?
Please make a two sided copy from your printer. This step will be a test, to verify a software issue or hardware issue. If this copy comes out perfect, then this would look like a software issue.
Also, please make sure you have the latest Firmware update on your printer. If you are unsure please click here. Make sure you select your correct operating system.
Let me know your troubleshooting steps and I will assist you further.