Sprint freestyle

Hi All. This is my first post and this question may have been asked before, if it has, sorry. Does anyone have suggestions on how to stay smooth when sprinting freestyle? I have noticed that when I do 25's or 50's fast, that my stroke gets sloppy. When I do middle to distances swims, even at fast paces, my stroke stays smooth, balanced and symmetrical on both sides. This feeling seems to go away when sprinting, esp. staying symmetrical. Any suggestions are most welcome! Thanks! John