Pix? banding is caused by so many different things, without a couple pictures it's hard to say exactly what's going on, even with them, it can be a challenge.
It's like going to the doctor and saying, I have belly pain, and expecting him to tell you what's wrong without him being able to examine you in any way.
As for color shifts, what RIP are you using?
Grays are notoriously hard to hit, cool gray in particular. Pick a swatch that most closely resembles the gray you are trying to print, then turn off color corrections, this should hold color as it's being assigned in your design software package. There is no hard and fast rule to color management, it is, and will remain one of the biggest challenges in this industry. If you're system isn't color calibrated in some form or fashion, you're lucky you get anything even remotely approaching consistent color. That's like asking a blind man to paint the mona lisa. IT could happen, chances are it won't tho.
