at the start of your tween span, move your object to the left of the stage, in the middle of your tween span, move your object to stage center and at the end of your tween span move your object off-stage to the right. test. is that doing what you want?
It moves from point A to point B fine, it's the slowing down in te middle thats giving me problems.
you said, "..it just goes back and forth". that problem has been solved, correct?
to see the effect of eases, use -100 and +100.
also, you might want to try different (than simple slow) eases