Help: sluggish shifting

In the past couple weeks I have been having hard time shifting. Shifting into all gears feel very sluggish. It feels like it gets stuck but doesn't produce noise. A lot of time I can't shift all the way and I need to pull back to neutral, release and re-engage clutch and reshift again in order to get it into gear. It seems to getting worse.

Could this cause by my clutch? The thing is the clutch doesn't slip at all. My car is a '01 with 50k miles, original clutch, out of warranty. And I don't abuse my car. :dunno: