I have a HP 932 Printer that has never printed pictures or color anything in a decent quality. The images almost always have pink lines running horizontally through them and picture quality is low.
Have you checked in the print driver properties. Some of the new HPs have a Digital Photography options in the Print driver when a photopaper is selected. These are normally "On" by default. I've seen green horizontal lines if these were enabled. Disabled the Digital Photography options and the problem went away.