Literally the exact same thing was happening to me. I just replaced the whole clutch assembly my self. And I haven't had a problem since then. I thought about upgrading too but at auto zone they have the whole assembly (clutch, pressure place, slave cylinder, and bearings) for $480. I had 120k miles on my clutch so I knew it was time to change. Also my master cylinder broke so I replaced that too. That was only $100 at autozone. If you replace your clutch you might want to look at getting a new flywheel or even having your stock one shaved. I didn't and it's working just fine, it's just your personal preference.