I think my clutch is slipping, but I'm not exactly sure as this is my first manual car. Whenever I'm in first gear and do a pull, after about 4-4500 rpm it just falls on its face and feels like it loses all power. But when i go to shift into second it will start pulling again. It seems like its only in first. PO said their was an LS7 clutch in their, but I've found out that some of the other things he said were in it are not. Has 86K on it. So is it my clutch or not?

 

Try putting it in 5th or 6th at 1500 rpms or so and hammer it. If the clutch is going to slip thats the time it will do it.
The rpms should shoot up and the car shouldnt accelerate, the clutch peddle will probably feel mushy too.

 

Just like the previous poster said, your clutch is under most pressure on high low load at low rpm's. See if that slips your clutch. When I first started messing with my car it wasn't long before the stock clutch was overwhelmed.... it would slip on the shift. That is, when you shift from 1-2, the rpm would drop and then come back up, and it would do it again and again. To me it sounds like you have something else wrong since you're slipping only in one gear.