I just set up a new MacPro with 10.5.3. Apparently Epson does not fully support this system in their current drivers for the 4800. I could only find a driver with limited capability and the prints stink. Completely wrong. Their website says the full driver will be available in March of 2008... Uh, it's already July.

I can't make good prints now. There's no going back. Anyone with this combo?

Figured it out. The driver from the Epson.UK site worked fine and is different from the one on the US site. Prints are excellent once again!