The trick to the Tantrum is to let the wake perform the trick. What does that mean you ask?
You want to progressively edge toward the wake at the moment you hit the wake, (I find it helps to hesitate about a half second when you clear the wake) let go of the rope with you back hand and center your head between your shoulders. You will rotate and will be able to see the water on the other side. Once you have done that the board will land and get ready for the pull of the boat.
Things that helped me
1) Video tape if possible and compare the video tape to how the pro's complete the trick. You will be amazed how much this helps.
2) Make sure the board your using is the right board. It made a huge difference in my wakeboarding by changing from an Obrien Shifty 132 to a Hyperlite Premier 142. It matches my weight better and I feel so much better on the board.
3) Keep working on the trick. I try to perform the Tantrum at least three to four times everytime I'm out boarding.
Believe it or not when you start coming closer to landing the Tantrum, it doesn't beat you up nearly as badly when you first start working on the trick. I'm also finding that it has helped big time with my backroll and I starting to develop that "Air Awarness" that is so important for all the other inverts that I will work on.
Hope this helps.
PS. Pick up the book Wakeboarding on the edge. They have a DVD that shows the Tantrum in slow motion frame-by-frame. This book did wonders in helping me to understand the mechanics of the trick.