Shaft Load

[iPutt]

Recently I went for a driver fitting, and one thing that they measured was the load/bend in the shaft at different points in the swing (I forgot the exact name for this). What they found was that I was releasing the load built up in the shaft too close to the top, right as I was starting the downswing, and therefore I was not transferring as much energy into the ball. He said I wasn't "casting," but this is one of the only ways that I can think of explaining this right now. I think that the best way to explain this is that I am accelerating too early, and not accelerating through the ball like I should be doing. So my question is, are there any drills or swing thoughts that I can practice to help this? I'm sorry if I'm not explaining this well, and if it's still unclear, I'll do my best to try and clarify things further. It's just killing me that I'm leaving club head speed and distance out there. Thanks for any help!

Edit: Just read the thread below this (Accelerating Through Impact) and I think the key thing that I took away is that my maximum speed* (speed is all that matters at impact, not acceleration) is reached too early in the swing, and that means that I'm decelerating into the ball. Hope this helps.