...had a similar problem ten years ago... turns out the pushrod on the slave had worn and mushroomed over, so not enough stroke to fully disengage the clutch causing it to drag and subsequent hard shifting.

Check fluid level as stated. If that's okay, it's time to remove the slave for inspection. I posted a thread on the subject, including removal/installation tips and how to bleed the clutch system with a new slave.

http://www.peachparts.com/shopforum/tech-help/94805-201-clutch-slave-cylinder-swap-post-mortem.html

Duke