Engine silky, engine edgy

[AMink]

This is kind of weird so I hope I can explain it right. Sometimes my engine is smooth as silk, great power. Sometimes it gets kind of "edgy". It doesn't run rough or miss or anything like that, just not as smooth. It's done this for as long as I can remember, even before I changed things around in the pump. I recently replaced the overflow valve and the rest is in my sig. It will be different during the same day. It won't change while driving, but if I shut it down then run it later, it may run better or not. Any ideas?