If DL's interesting tip doesn't get you all the way there and Premium Luster is too expensive, you're going to have to find an alternate paper that works for you. Epson's Photo Quality Inkjet paper is one of several they produce for use with their (budget) dye ink printers that just won't meet your needs. For my daily photo printing I happen to use Premier Art Premium Photo, which is a Premium Luster work-alike available locally for a fraction of the price.
need to give printouts of our designs in *accurate* colors to our fabric manufacturers
If you have a fully colour-managed and profiled workflow you can achieve accuracy with your 4800 ...
within the limits of the paper+ink combination you've selected. Photo Quality Inkjet paper together with pigment ink has gamut limitations that esp. include not being able to reach true black.
All papers have inherent gamut limitations; but I would imagine that mostly the gamut of the better papers will include the complete gamut of textiles. Pigment black happens to be the most serious issue.
So am I just not using the printer right, or am I screwed?
The 4800 includes cutting-edge technology to ensure that the supplied profiles for Epson branded papers are highly accurate (within their inherent gamut limitations). This is a very mature design compared to competition like HP and Compaq. So I doubt there is another wide format printer you could have bought that would have been a better bet.
If you decide to opt for a third party paper, such as Premier Art Premium Photo, try using the supplied Epson profile for whatever Epson-branded paper is most similar. In this case that would be Premium Luster. If colours are not sufficiently accurate, you will need to have a custom profile made for that paper+ink combination. Once you have that done, thanks to the accuracy of the 4800, you should be set for years to come so long as you stick to the same paper.
If the above doesn't help ... well, you can muck around with hit or miss solutions for months or years and sink a big pile of moola in the process. You've been through printer choice and now paper choice - how many other gotchas are waiting ahead? What you really need is to bite the bullet and hire a professional colour consultant as a one-time expense to get you up and running. Andrew Rodney (
digitaldog.net) is one I happen to be aware of that you can contact via the internet. I'm sure he (or someone like him) can recommend the most appropriate paper, profile it, profile your monitor, work you through the intricate maze of Photoshop settings, etc., etc. An up-front expense, but one that would almost certainly save you considerable money in the long term.