Some additional thoughts on this issue...
@larkis: You mentioned that your scanned color test images were printed using Photoshop, which implies you are printing using the Epson driver. I'm not sure of the source of your test image, but it is unlikely that the color bars are actually being printed with just a single ink channel, even after trying to tweak the RGB values in Photoshop to approximate a single Epson ink color. The only way I know of to actually tell the printer to print using a single ink is to use QTR or a RIP that allows ink channel control directly. (BTW, are you using Epson inks/carts or something else?)
So given the above we should not exclude the possibility that other ink channels could be contributing to the problem in your "light gray" and "green" bars in the Photoshop print. Looking at your nozzle check JPG (it's a bit hard to judge this on a computer monitor) both LK and GR appear to be OK, but I do see what could be a deflecting nozzle in the Vivid Magenta (about 2/3s down from the top). I would get a good loupe and take a detailed look at the VM pattern to make sure everything is clean. If not, I'd recommend clearing that up before trying other things to solve the banding in your gray and green bars. It wouldn't surprise me if there is some VM in your light gray bar, but probably less likely in the green bar. Even in ABW mode Epson uses magenta and cyan to make the prints more neutral, so that could explain why you are seeing the issue in ABW (though less pronounced). Anyway, I think it's worth double checking all the nozzle patterns with the loupe, especially the VM.
Apart from the above, the only other thing I can think of here is that there could be some ink starvation going on in certain dampers in your Ink Selector. If all other possible remedies fail, then replacing the Ink Selector might be worth considering.