To the original poster, I can appreciate your frustration! I certainly felt the same way early in my implementation of GTD.
If I may offer a blunt, contrarian view:
It takes time.
You will not get everything out of your head immediately. You will not have a pristine working system quickly. Your brain isn't going to rewire itself in a few weeks. It can take months to re-orient your life around a new productivity system. Heck, it's taken many of us years.
This is frustrating. This is hard. But it's just how we're built.
The rewards are worth it.