After seeing that re-profiling my printer with Prism helped the posterization of shadows I was getting using the cheap Kirkland Glossy Photo printer. I tried the same thing for my Epson Premium Luster paper, which is my perfered archival paper.
I had recently paid for a Cathy's professional profile which was fine when I got it but now was seeing the same posterization effects in the shadow areas of prints.
Creating a new profile did (PP2 - PLuster), in fact, improve the prints. So what's the deal? Is the printer color output shifting over time? My test prints show that all nozzles are firing. I'm starting to believe my brother who says its the third party inks I'm using, even though I have read people having the same issue with Epson Ink.
One to watch for now, I guess.