[FMX/2004] fadeIn prototype, run by multiple objects at the same time

I have the following prototype, which is used by typing objName.fadeIn(100, 3);
this is all well and good, although when I start to use it on multiple mc’s at once the playback becomes quite choppy and nasty… any ideas dudes?

MovieClip.prototype.fadeIn = function(v, r) {
	this.onEnterFrame = function() {
		if (this._alpha<v) {
			this._alpha += r;
		} else {
			delete this.onEnterFrame;