sr20det clutch probs?

hey all. I have just been in the process of buying 90 240sx with redtop. I was told by the owner that the clutch slave was gone. The problem is that at about 4000 rpm the clutch will slip and the car wont go any faster. Correct me if im wrong beacause i am a noob, but wouldnt the slave just be working when the clutch is engaging? Suposedly its a new clutch on it so i guess we can rule that one out. Any idea what it could be? Could it be the discs? Or mabee fluid is leaking onto them? Any help would be awesome. Thanks guys

Clutch is probabaly on it’s last leg, or the master has be adjusted incorrectly.

Slave cylinder will only push to disengage the clutch. It shouldn’t cause the clutch to slip when it’s fully engaged.