Hello everyone!

Well I've recently purchased my '87 trans am from my brother. About a month after I've been driving it, the clutch started to develop a slip after about 1/2 throttle travel regardless of the gear it's in. Normal driving it isn't a problem but if I want to "put the hammer down", it just slips. The funny part about all of this is that it doesn't just slip all of the time. Every once in a while I'm able to go full throttle with absolutely zero slip. My brother did replace the clutch when he first purchased the car about a year or two ago and it worked fine up until now. It's been riding with this slip for about a month now and I figured if it truly was simply needing a new clutch it would have gone completely by now. I'm hoping that it's just the slave cylinder or something but I'm just stumped. Any help or information that could be useful would be greatly appreciated.