there are several things it could be , pressure plate binding , clutch disc cracked and spring trying to pop out , those models were bad for that, clutch hydraulics not bled properly, also in 99 and 2000, year models seem to be the worst for eating up pilot bearing bad ,and also last but not least the clutch fork inside the trans the release bearing rides on would also crack or bend , there is a updated part for that , so in saying all this what im getting at is the best thing for you to do is remove the trans and inspect all the components and then go from there