I've had it happen and found I wasn't printing true black.
What program do you print from? If I print from Signlab through Accurip, it is VERY easy to get what you're describing.
Also, CMYK produces a different result than RGB for me. I usually work in RGB for that reason in photoshop. RGB values are 0, 0, 0....but there are SOOOO many ways to skin a rat in this biz.
I am on my 2nd 1400. PM me if you can't figure this out and I'll call you on the phone.
Stan