Periodic Cleaning??
Perhaps your periodic cleaning setting has changed??
MENU > SUB MENU > PERIODIC CL
The default setting is NONE, but you can set it to:
PAGE (Performs a cleaning before each page) or a TIMED SETTING from 10 min to 990 mins. (i.e. a 10 min setting means the printer stops and does a cleaning every 10 minutes while it is printing)
Timed period cleaning can help if you are getting "ink drops" collecting on the printheads and dropping on the media, but it can cause visible "dry lines" or unevenness when printing solids.
Hope this helps!
~E