It's possible to have what appears to be a perfect nozzle check, and still get banding from misfiring nozzles. I've had this at least once. Take a look at this InkJetMall article:
http://www.inkjetmall.com/tech/content.php?167-Evaluate-a-Manual-Nozzle-Check-to-Determine-the-Health-of-Your-Printer
In the discussion on resizing, it's not clear who is working on Windows and who on MacOS, because this makes a difference. As Roy Harrington has explained on the Y-QTR group, QTR expects 720dpi. If it doesn't get it on Windows, then QTR will do the resizing / resampling. I've recently compared one print where QTR did this, and another where I resampled to 720dpi using Qimage, and the Qimage image was slightly better, but I had to look really carefully to see it. Certainly no signs of banding either way.
However on MacOS, which I rarely use, it's my understanding that the resizing is done by the printing pipeline, and it's also my understanding that this resizing is not all that high quality. So that may be a cause, and if so, resizing in Photoshop should fix it. But if you are on MacOS (10.6.8 or later), in general you shouldn't be printing direct to QTR from PS, because in addition to the resampling issue, there's also a colour management issue. Use Print Tool to print.