How is your humidity in your print area? Are you keeping it above 50%? this really makes a difference in the way it flows, if the air is too dry, it will cause banding and basically just bad printing. Also when you changed your printhead, did you also change your dampers? it could be buildup in them. If these things are fine, I would look at your capping station, make sure it is really clean around the seal. If none of these things work, it could be your capping station needs to be replaced. Hope this gives some idea of things to check.