I'm going to guess you have a bad clutch master cylinder. Often times when they leak it doesn't show up because the fluid is leaking past the seal and it just goes into the fluid reservoir. I had the same problem with a Mitsubishi eclipse. One way to find out is to pump the clutch lightly just at the very top of it's travel. If it improves your shifting, you have a bad clutch master cylinder. Which is an easy fix. Hope this helps.
