I came across this thread while I was experiencing the same problem: networked 3800, 10.5.5, excruciatingly slow printing where it pauses after every head pass. Although this thread was resolved, I thought I'd add to the thread since my solution turned out to be different. Perhaps it might help the next person who has a similar problem...
Anyway, I was having general networking problems, probably due to a recent logic board replacement, and had lost all communication with the 3800. I did a bunch of driver install/updates, printer add/delete, etc and finally got it working... except for the slow printing problem. I finally discovered that if I connected via Appletalk, I got the slow printing, but then if I added a new printer with the "Epson TCP/IP" version it printed fine. I had added the Appletalk version because the TCP/IP version wasn't showing up, and then did later for some reason. Anyway, something to check for...
j