Yeah, I'm guessing it's a print head issue. Once the new head comes in, I would simultaneously put in a new Matte Black cart and see how it goes. Get your critical print done, then began working backwards, trouble shooting the problem. I would definitely NOT put the original print head back in after you've replaced it though, even if curiosity is killing you. You should be able to swap carts, however, in my experience. Run head cleanings, after, etc., and you should be alright, is my guess. BTW you should be able to target just the suspected offending head with cleanings. Good luck -
-Mark