So my question, by setting CS3 to "No Color Management" is the Epson driver reading the tagged info from my file that I saved in CS5?
I’m assuming that the document shows as Untagged RGB. Keep in mind that whatever RGB working space you have setup in your color preferences is the assumption for this untagged data. So it is possible that if you had sRGB set in CS3 but another working space in CS5, you’d get different results. Photoshop doesn’t really have a ‘no color management’ mode. It always makes some assumption about the document color space.