First, let me respond to Peter. Thanks for the suggestion, but I had already tried that with virually no change.
I tried printing from my laptop that runs on ordinary Windows XP. Unfortunately, I found the same problem printing the file to the 4800, so it doesn't appear to be x64 OS related. I spoke to Epson again after this. We tried printing another image -- an Adobe sample image, I beleive, and I still got bad color blocking and a solarization type effect. Epson, after all we tried, could not explain what was going on. The only think left to try was doing a complete head alignment. Epson is going to call me again on Monday to arrange a printer replacement I did the complete auto alignment routine for 4800 and then tried to the print again -- a minor, if any change at all. So, no real success. I printed the image again on the 7600 for comparision (both were printed with the Epson drive color control, not by photoshop) and it came out as it should. On a lark, I then tried another picture on the 4800 and lo and behold, it looked pretty good. Now I really don't know what is going on. Was it just something about the original file (lots of OOF areas, perhaps?) that the 4800 just could not handle? I then printed the new picture on the 7600 the same way as on the 4800 and it came out pretty close to the 4800 (a little lighter + cooler due to Ultrachrome vs. K3 ink, and MK ink vs PK ink on the 4800). This is consistent with what the Epson tech guy said -- that the K3 inks print a little darker than the 7600 inks.
So now what?? Is it possible that the 4800 just doesn't like -- or can't handle -- the original image? The following 2 images hopefully will help you see what I am seeing.. The first, the original image that caused a problem for the 4800 (the 7600's output is virtually identical to this, as it should be). The second is a scan of the last printed output from the 4800 of the file (some of the prints from the 4800 were actually worse than this -- even more solarized and muddy).
Something screwy is going on. I've got until Monday to see if I can figure out what is going on. On Monday I will have to decide if I let Epson take it away for a replacement. I'll print alot more tests with it over the weekend. Any suggestions, thoughts, or particular tests I could run?
Thanks for all the help. I really appreaciate it.