any news on your problem? I have been getting the same thing for the past year on my jv33. I have also tried everything that you have. I even took off all of the roller and soaked them in water with alittle dawn dish washing soap and scrubbed them with a tooth brush. I printed some test prints and they were not there. It seemed to fix it but the next day i loaded some 3m ij35c and they were back. my test print is almost perfect. Luckly I have another printer that i do all of my dark color printing on. and just use the jv33 for lighter colors.
No luck here. Still have the same problem regardless of the print media. I only use Mimaki ink. It's driving me crazy...