I believe tongue twisters do help. I use them myself. However, they are more effective if you can practise situating your voice in your body. Such as deep breathing and doing the kind of warm-up exercises with the voice that stage actors do. There may be a program on-line. I have been a stage actress (who stutters in every-day speech that is not memorized) and I find that doing the vocal exercises with the breathing and adding the tongue twisters does help.