Sick of my tweens not being smooth. Please help?

I am not understanding why a simple alpha tween is staggering my processor every time and just making the tween seem slow and not smooth.

I basically have a black movie clip that covers my screen, and i want it to fade up. I’ve tried using mctween for this and on the timeline, and it doesn’t seem to make a difference.

the fact that it’s large shouldn’t really matter, cause it’s all vector.

i feel like on some high end flash sites, i see really nice, smooth tweens all the time. But why is it that mine seem so far away from that?

I’ve looked at cacheasbitmap, but is that the answer? My frame rate is 30…and I don’t have all sorts of animation at the same time.

What are the tricks to get just really smooth tweens?

Thanks.