When I first got my Gracie I was having the same problem, her coat seemed dull and it did not shine
. I had bought her the Pet Silk shampoo " Phase One for Fine Low Volume Coats Shih Tzu, Maltese, Yorkies, Silkies, Afghans, Saluki, similar coat types. and when I bathe her for the first time, let me tell you it did wonders for her coat
. They also have other products that can help like 'Silk Sheen" that it texturizes and revitalizes dry hair and skin, detangles and adds gloss. You should checkup this website.
Hope it helps.
http://mjm-petsilk.com/catalog.htm#mjmlink2.jpg