50 mph change"
When you say can't control them do you mean throw them for strikes? 20 mph difference from a change to fb is a mighty fine difference...don't expect it to be a strike, let it hit the dirt, if when you throw it, it looks like your fb, then you will strike out everyone in sight. And for the slide piece, same thing...figure this...you are throwing strikes with the fb, and both the slider and change should look just like a fb, so the batter sees a fb looking pitch and has to assume you are controlling it like you seem to do on all of your fastballs....if the slider breaks out of the zone you'll either get a poor bat strike or swinging strike......All pitchers should have your problem there slick. You just have to think about it as a dominant pitcher should think about things.....At your age having a change and a slider is pretty good just to be able to throw them....It's just absolutely critical that you make them look like your fb and watch the W's roll in. That is unless both are obvious and hitting the backstop, then you have another issue all together.