I would recommend you a technique called mirroring which is basically copying someone else's gestures, rhythm, stress and intonation while talking
you play a video of someone talking , (you need the script) and you start saying the same words at the same time as the video, once you are comfortable saying the whole thing you can avoid the video and start saying the same words but without the video this time.
It is basically like doing karaoke ,but talking instead of singing. (personally I love to sing and I like to practice my speed with some songs, at the beginning some songs feel like a tongue twister but with time it's easier )
Hope It helps.