[SWHouston]

From what I read, it sounds like he "gets" greasy after a while, as opposed to "is" greasy after baths... ummm

Apparently he's getting some good Nutrition or the opposite would be the case. Many with this or similar problems, use Dawn Dishwashing Soap as a preliminary wash. You also must consider that you are exacerbating the problem with the existing Shampoo not being thorough, or a Conditioner re-applying some (what they think are) necessary oils which are presumably washed away.