EPIK

I have a 2005 CTS-V with 58k miles. I purchased the car with 50k miles & all was well until roughly about 2k miles ago. The clutch pedal seems fine in normal driving conditions, but when I drive the car aggressively, the clutch pedal goes dead in the high RPM's to the point to when I try shift to 2nd, 3rd, or 4th, it's completely dead & I will miss a shift. The previous owner tells me that he installed an LS7 clutch kit along with an LS7 slave cylinder at around 48k miles, but he didn't replace the master cylinder.

Does my problem sound like a clutch issue, slave cylinder issue, or a Master cylinder issue??? I don't want to just throw parts at it because I'm on a strict budget, & I personally don't know how to properly diagnose this issue. I did have the fluid bled recently, & this didn't help. It actually made the issue worse because now when I start my car up for the 1st time on a cold day, I can't get the trans into reverse unless I turn the car off & put it in reverse before starting it up? Once the car is warmed up a bit though, I can easily get it into reverse....

Any info you guys can offer will be much appreciated.... Thanks in advance