Try a dandruff shampoo called Nizoral. I had hair just like yours, if I didn't wash for a day or two it got greasy especially at the roots, but the dandruff would still flake off. Aside from washing daily (which I found would damage the hell out of my hair when it was long) I used this stuff.

It worked wonders for me, it's available OTC in Canada but I'm not sure if you still need a prescription for it in the states. It's pink and kind of funky smelling, it kills a fungus that can cause dandruff.