I get horizontal yellow lines all the way down the page with my epson stylus dx6000 all-in-one printer on all pages printed.

Not sure if the situation we're in is the same. I have a similar problem, but instead of yellow lines, it is pink lines. printer is Epson RX510. The lines are more prominent if the print quality mode used is best and if the document to be printed requires the affected color. Upon consultation with the printer technician, I was adviced that it is the print head which has a problem, and changing it is costly and the repair duration even depends on parts availability. With that, I just decided to use the printer just as is. Hope this info helps.