I would suggest you run the fill test under test pattern in the print menu in service mode. If you aren't familiar with it, it prints each head individually at 720x720, 8 pass, bi-dir, 100% ink. No profiles or images, just each head running full blast at pure ink color. Watch it constantly while it prints and shine a bright light on it while you do. You could run it, wait a bit and run again, or run it multiple time in a row. Since you have an i1pro, you can also take spot measurements and see if you find any inconsistencies in density. I would also suggest you use your i1pro for troubleshooting this issue. Measure the same exact areas on the prints that have the color deviations and you should be able to see what colors are changing. Think of it like a multimeter for color...