Clutch problem

[ticopowell]

Ok, Question for anyone that knows anything about my mustang, details of the car are listed in my sig.
The car's clutch has been acting weird, sometimes it feels like it isn't engaging/disengaging. A few times while I have been driving it, right after I start the motor I can't get the car into gear, any gear, with the clutch pedal pushed to the floor. About 3 other times I tried to start the car, the clutch was in all the way, and the the car started moving when the starter motor was engaged.
Both times it acted like I wasn't pushing the clutch in.
All I could do to fix the first scenario was to turn off the car, pump the clutch(this didn't appear to fix anything as far as I could tell), and then start it in gear. The problem starting in gear hadn't happened yet, so I didn't think to not put it in gear.
In the cases where it started moving I stopped the starter, pulled it out of gear, and it started right up and went into gear without issue.

Any ideas?
I would think it was low clutch fluid, but it still engages and disengages normally most of the time. Actually brought the car to the drag strip in san antonio, best time of 14.5, and it had it's problems once there, but we got it working again pretty quickly.
Could it be the slave cylinder or something related? The clutch and flywheel are about 6 months old now, I didn't replace the slave cylinder then, I didn't realize at the time that it was recommended to do, so does that make sense that it should be replaced?
Other than either of those two ideas, I have no idea what could be wrong, so any help, or guesses, or ways to save me money, would be appreciated.