Hello doors42,
It sounds like you may have already tried what you can so it may be time to contact the Support Department - 1-800-821-2797.
I have a versalink C400 printer. When printing from Word or the web the black is faded but it is not faded when pringtin PDF's.
I have replaced the cartirge, changed the paper, adjuted the colour settings in the printer and in Chrome, cleaned all the bits as shown inXerox's video, adjusted all the setting I can in the driver and finally reinstalled the printer driver with a new one from the Xerox driver page today.
Nothing has helped and the black is getting fainter and fainter.
Help, please.