i just completed a print on 13x19 silver rag, there are splotchy areas that are lighter than the surrounding area. i don't detect any particular directionality to these splotches, but could it be that i need to change the print head height on my R2400? could these be coming from the print head hitting the paper. i'm using the manual-roll feeder and i select epson premium luster in the printer driver, best photo. they are not all over the print, but clustered in certain areas.
i in fact printed the same image again only on actual epson premium luster using the sheet feeder, and no splotches.
I may be misdiagnosing your problem, but I get better results on Silver Rag using the Premium Semigloss driver setting. At least with my printer (also a 2400), the Premium Lustre setting lays down too much ink. You might also try decreasing the ink density incrementally and see if that helps.