For me, the problem first appeared after the installation of the driver for the 7800. It seems that way for you too with the 3800 in early February and the recent 4800 - is that correct?
I think so but there's some hesitation (and a lot of wasted ink and paper) as I'm just not sure what causes this mess and if there's a long term fix (other than doing the default trick which does appear to work).
I called my bud Mac Holbert at Nash Editions. He's having the same problems and noticed them months back. He's be using the Default trick (in Printer Utility) and says the problems are gone.
As to the old switch-a-row with the profiles in ColorSync, I'd like to test this on a few other Macs and also see if the connection (USB versus Network) has any role (I don't think so).
And as you point out, installing a new Epson driver could be an issue. The 4800 is new on this one Mac and since I'm waiting on a network card, its USB. The other Mac's are clean (didn't get install the Epson drivers). Then there's the fact that one machine is an Intel and the other PPC (I don't think that's a factor).
Now here's another test. Substitute the 3800 Standard profile in ColorSync with the 4800 (or vise versa).
I'm almost ready to just use the Default Printer Utility trick because all the variations here add up to a lot of wasted ink and paper! And you never know, Leopard may ship and the entire issue may go away (or get worse).
Bottom line is, if we know users have more than one printer and are using an Epson (some, all?) on a Mac, they should be aware of the Printer Default trick or they may end up with issues on some images with subtle reds of certain hues. And making or using custom profiles? Ouch.