Hello lasercode
Why don't you try to use onComleteAll instead of onComplete:
function tweenScaleUp():void {
TweenMax.allTo(stepArray, tweenSpeed, {alpha:1, scaleX:1.5, scaleY:1.5, dropShadowFilter:{blurX:15, blurY:15, distance:5, alpha:0.33}, ease:Cubic.easeInOut, onCompleteAll:tweenScaleDown}, stepStaggerAmount);
}