Re:Crack my cake
It's possible that you're overbeating the batter. Chemical leavenings begin to work when they touch liquid, so if you beat the batter too long it can definitely affect the volume. I don't know if that's the problem, but you might try less mixing.
Another thing you could try are cake baking strips which you can add to the sides of your pans before you bake. I don't know how they work, but apparently they can keep cakes more flat on top, rather than peaking. There are several vendors for them--just google it.