I to have that problem, the best thing I have found is after installing the new inks is to leave the printer on over-night.
With regards to Epson printer's, I have found over many years of use,that if left unused for any longer than a few days the ink causes vertical line printing on all paper types.
The best advice is to use the printer more often.
Or keep it turned on as much as you can, even if you are not printing.
gary, October 2006