You should be able to lower the resolution BUT print 'Uni-directional'. That will usually help the banding and keep the speed reasonable. Printing High Resolution AND Uni-directional is REALLY slow (If that concerns you).
The only other option is to try selecting a different, but similar Paper Type and see if that helps.
I assume you have already printed a nozzle test and that was clean.... I hope you did. Else you would need to do a 'Head Cleaning A', under Maintenance. Don't run the Head Cleaning B, it's just a waste of ink. And don't do more that 2 Head Cleanings at one time. It can over heat the Heads and cause more problems.