How can I get a clearer voice?

Okay, well I am attractive and intelligent but I know that people can't take me very seriously because I have an extremely annoying voice. I always slur my words and stutter, I mumble, I have a lisp, It is kind of high too and it sounds very childish and for some reason I always need to swallow. I always feel insecure about it and it is ruining my self confidence. How do I fix this? And Ideas??? Help! Please!!!