I have always had problems in this area. The problem is that by using too much power I was being stiff, and aside from using too much effort to no effect, was actually getting in my own way, since being stiff like this kills your sensitivity -- your ability to feel how your opponent is moving and respond to it. It also makes it real easy for your opponent to feel how you're moving and respond (ouch!).
For myself, what seemed to work was to take a step back and practice the techniques slowly and lightly, without intent, as if I had never done them before. I try to do it this way with everything now, working on smoothness, before adding speed or power. After a while, as the technique starts feeling more natural, you can sort of feel the best time to start putting energy into the motion, so that it does what you want. You can absolutely perform a technique with intent while being soft -- soft doesn't mean limp, it means you're moving with your opponent, leading them to their destruction.
That said, there are times when the right thing to do is a blast-through-their-defenses, purely offensive action, but even this needs the sensitivity to know when and how its best to do it.
So, pretend you're a complete beginner. Practice the techniques slowly and lightly. Try not to rush. As you feel more comfortable, still do them lightly, but start adding a little speed, keep adding speed. If you're anything like me, you'll start going too fast and getting a little wild. What I do then is slow down and lighten up some and concentrate on precision and slowly add energy -- this is where the flow drills are so useful, especially if you have a partner that is better than you and can go as fast or slow as you.
Hope this makes some sort of sense.
