Hmm....without knowing more about your hair care routine, I'd have to suggest clarifying in some way. Like a clarifying shampoo, vinegar rinse or both.

Conditioning is essential, but apply it only to the length - not to the crown. Condition from about the ears down, concentrating on the ends.

I had a similar problem with Pantene's Daily Moisture Renewal products. They changed them a few months ago and they gave my hair that terribly greasy, "stiff" feeling you described.

After clarifying, that usually goes away, but sometimes it can take a few washes to get all of the "gunk" out.

Hope you find something else that works.