Dejan, I know what you mean. When I started playing all I wanted to be was fast, and I got pretty good at it. But when I would play something slow, I found it extremely hard to be precise with my timing. I was always alittle ahead of myself. But as I worked on a slower tempo and got better at it. I would go to back to a faster tempo, and I was alittle bit quicker. So I rethought my whole plan of getting to be be faster. Here's what I came up with.

It's better to start at a slow tempo (say 60bpm, I know thats extremely slow but just go with me on this.). It will help you build a better sense of time right from the beginning. Cause at a slow tempo their is a bigger span of time to miss a beat, forcing your rhythm to be more precise.
Once I became precise with that tempo I would slowly go up speed, making sure my rhythm was precise as possible. I did this with every scale I learned, and now I can play everyone at any tempo with almost perfect precision. I believe it's better to start with a slower tempo and work your way up to faster tempos, rather than Vice-versa. Like the good ol' saying, you have to crawl before you walk.

Hope that helps.