Although I'm also not a fast calculator, the main reason I used to be so slow was that I was simply overwhelmed by the possibilities for each move, and had no idea what to prioritize. Now that I've gotten some experience under my belt, I've developed a (semi-unconscious) set of priorities, and it's much easier for me to find a move. I no longer feel overwhelmed and instead usually have an idea of what I think is important. Basically, I've played enough games so that I don't need to agonize over every move. On the flip side however, I have also learned to make the same mistakes again and again.
Why? Because my priorities were probably good enough to get me where I am, but not any further. Now when I calculate, it's because I'm trying to find the best way to do what I want to do. I still need to improve my calculating, but who doesn't. The real problem is that I have developed some bad habits, but strategical ones and tactical ones.
What I suspect Shapenaji is getting at, is that now I've given myself the chance to develop these bad habits, it's probably easier for a stronger player to recognize what these false assumptions of mine are. So, the flaws of my game are now out in the open - I just need someone to point them out to me.

Patience, grasshopper.