Dear young lady, speech patterns are signature of a person. Every person has a unique style of speaking and yours would be unique to you. However if your speech becomes unclear to the listener I think it is time to alter it for the listeners benefit. Since you say that to some people you speak slowly and an under stable tone I would suggest that you practice and use it across all persons. One if the methods to practice is to use the mirror and speak there. Since you have decided to make a change I think consistent and dedicated effort will guide you through. Best of luck. Hope this helps you..