I have heard that you should first master alternative picking and then go to economy. I used to play the same way -- I played everything using economy picking and I when I was practicing speed exercises I could not go above 140 bpm. Then I started practicing alternative picking and now I can play about 200 bpm.
I'm not sayin that economy is wrong but from my personal experience and from what i have heard from others it is best first to learn to play alternative and then economy