I've had a lot of succes with AMLR running to FC, this makes them operate as a winger when the ball is on their side and a striker when the ball is on the opposing side, you also need your midfielders to follow up the attack, wether it's one AMC or two MC's running up to provide support, the 4-3-3 needs the midfield to win.
basicly look at a few games on full detail, look where your play breaks down, realize that maybe you need a DMC so you can push up the fullbacks, or maybe you need a AMC to run havoc infront of the defense.
Your striker might only have long shots and no "tap-ins" this could mean that the delivery system to him is bad, are your midfielders creative enough?
the 4-3-3 is completely different from the 4-4-2
imo, the 4-3-3 relies on the central midfield to dominate play and set up the offensive players, while the 4-4-2 usually tends to play down the wings to get in a cross. If you are loosing the midfield battle something has to be done.
Look at how Barcelona plays 4-3-3, the wingers (messi ronaldinho) are usually not involved in building the play, this is left to deco, iniesta, xavi and to some extent marquez.
IMO a 4-3-3 the wingers need to have better dribbling and flair than in a 4-4-2, but can get away with slightly worse crossing unless of course you play the huge targetman on top.
also check that your mentalities are not to far appart, especially between the striker and the AMLR. Creative freedom should not be set to high either, start low and then build it up to suit your players.
IMO mixed passing for the creative midfielders are a good option with short upfront, maybe short-mixed on the wingers, the backline is purely down to what players you have.
Enjoy the tweaking