Thanks for your interest! The tests I described above were done is the same way as yours. I created a small Adobe RGB document and filled it with RGB = 162/199/255. In Customize Proof Conditions, I set Device to Simulate to the profile " Epson Stylus Pro 3880_3885_3890 PremiumLuster", Rendering Intent to Perceptual, checked Black Point Compensation, and checked Simulate Paper Color. If Gamut Warning in the View Menu then is turned on, no gamut warning appears. If I attempt to print that document using that profile and click on Gamut Warning in the Printer Settings menu, no gamut warning appears.
The profile in question is the standard Epson-supplied profile for Premium Luster paper on the 3880: the header fields as displayed by Color Think are shown in the attachment. If this is the same profile you are using, perhaps I should try replacing my current 3880 profile package. Any suggestions you have would be greatly appreciated.
Thanks,
Mac