Kodak PPP has a rather bad reputation of creating a "craked mud" effect, or sometimes called micro-pooling. I believe this is the grainy effect you have mentioned.
When I first used it, I got the same problem until I used an ICC profile created for this paper to work on Canon S9000 printer.
The reason for the micro-pooling is possibly due to the slow ink absorbtion of the paper. The profile I used required the media type be set to high gloss photo film.
Try a glossy photo film setting if you have that on your Epson driver.
However, I doubt if the colours will come out correct without an ICC profile.
Kodak PPP is a great paper if you can "tame" the micro-pooling effect and get the colours correct. I find it brighter and whiter than the standard Epson Gloosy Photo Paper.
- Roy