[8hnpSS]

Ive been chasing this issue for while I cant figure it out. Let me start off with if I leave the car sitting for 2-3 weeks it becomes very hard to shift at first. Once I drive 5-10 minutes it starts to shift like normal. In neutral the gearbox is smooth as butter and shifts like butter during normal driving. At WOT it will grind 1-2 pretty bad. At times it will lock me out of 3rd completely or grind into it at WOT. If I slow shift it at WOT sometimes it will grind and sometimes it wont. Every other gear is fine. I already replace the master cylinder with the Tick master it hasn't changed anything but make the clutch peddle a little firmer. Fluid level is where it should be, no chatter at all with the clutch and no clutch slip at all at WOT. I was told the clutch is stock from the previous owner. Car has 74k on it. Im not sure if I should replace the slave cylinder or should I start thinking of getting a new clutch? Internal trans issue?