1999 BMW 320 Clucth Shuuder on new clutch

I have recently had my car serviced and repaired. Included was a new clutch fitted, I am told the fly whell was fine. I have done about 15000km since and have developed a terrible clutch shudder. I would have though the clutch was worn, but it can't already be that. I have noticed that if I pump the clutch in the evening, it is better the next day, but comes back with in a day or two. I have tried bleeding both the brakes and the clutch but it now does not seem to want to get better. I am convinced it is something to do with the hydraulic fluid as it seems to come and go. A furthger sysmtom is that I can release the clutch smoothly, it always seems to jerk into placed and cause a knock on the diff and then shudder as if the clutch is slipping. I have place the car into 4th gear, reved the engine and let go of the clutch, probably not the best thing for it, but the cars does stall and the clutch does not slip then which prooves the clutch is not worn. Any ides?