Yesterday I spent some time testing your setup, by installing Photoshop CC on my new 10.9 laptop, and printing to our 3880 set up with ConeColor Pro inks with the latest print driver, downloaded from the Epson site.
Although I'm using 10.9, and you're using 10.9.1- my results came out as they should. I printed with both the Epson profile, to match your workflow, and with our CCP-3880 profiles, and both gave me great results.
So- the variables are the slightly different OS you're using, and your printer. I also discussed your situation with Jon, and he agreed your issue is very strange, and unlike anything we've heard of or seen before (I have had strange and overly light output due to a stale print driver, which was fixed by reinstalling the driver- but this is not your issue).
My thoughts are: 1. something in the new OS or driver has been programed to sabotage output for people using non-Epson carts, 2. your printer dampers are a few years old, have particle build up that's filtering the ink, and need to be replaced, or 3. something electrical or other mechanical issue with your printer is causing the sudden light output, and the printer to not print at 2880dpi.
The fact that your printer doesn't print at 2880dpi makes me suspect there's something more going on that an off setting or filtered ink, etc...
Jon suggested reinstalling a set of Epson carts to see if the problem continues or resolves (playing on the theory that Epson may have finally programmed a sabotage code in their latest drivers when detecting non-OEM carts), or possibly trying another Mac with older OS or Windows computers.
Please keep me posted, as I'm curious what's causing your washed out prints, and let me know if you have further questions or there's anything else I can help you with.
Best regards~ Dana