If you are getting a whole string of 100's or 50's then you are either starting the stream a little too early or a little too late. You could have your mind STUCK focused thinking that 1 sound in the song could be the start of the stream when it could be something else. I suggest watching some replays on whichever map you're working on.
I would also suggest to NOT do slower streams. If you're like me when it comes to streams (and it sounds like you are) it's much easier to do faster ones. Play some stream maps and when you find a fit that is good for your natural speed work on that map. When you can consistently do well at your natural stream speed then you can lower it or speed it up with new maps.
My top ranks don't really show it but ever since 2 - 2.5 stars a year ago i could stream quite well. But that doesn't really matter when you aren't fluent in AR9, squares, triangles, jumps etc