I don't want to be the bearer of bad news, but that was one of the symptoms I had right before a whooooole lot of visits from Epson. They were unable to narrow down specifically what caused it and ended up replacing main board, the aidboard, the pump cap, the wiper, adjusted the platen gap, paper feed length, replaced the print head, and finally replaced the sub board on the carriage. It got to the point where this odd cyan band (and sometimes a light band and sometimes just a 1/2" area of the print would be skewed before resuming normally!) would show up at odd places and at the worst times, always on enormous prints of course.
That being said: there are a number of things that I would check first to eliminate a few less expensive possibilities.
--Update your firmware.
--Hook your printer up to another computer and send a print. You need to make sure that this is not a computer issue.
--Try a different USB cord to connect to the printer.
I remember that for us, this problem was intermittent, thus making it more frustrating. I hope you figure it out...