When I was younger, my mother often said I had to watch my tone of voice. I a . I don't remember actively trying to improve on this, but she stopped. I'm not sure I ever understood fully what she meant, but then, it was a while ago. She also said, at around the same time, that I should look at her in the eyes. I never knowingly corrected that either, and she also stopped complaining. So I guess it's possible she just surrendered, or otherwise that I didn't notice getting better.
I often speak too loud in public (or in general, probably). That, I do notice. I don't remember being clearly told I was speaking loud, at least personnally (people have told me and a friend we were speaking loudly, for example, but not me specifically).
I don't think I have a monotone voice, except probably when I'm anxious, because, well... I'm anxious. However, my speaking speed varies between extremely fast and hesitating internally every three words, but saying these three words extremely fast too. Although I won't speak fast when I'm anxious, I am not necessarly anxious if I speak slowly.