I always talk really fast or slow and prononce stuff wrong and mix up words! If I did have a brain tumor/ cancer could I die?

Brain tumor. The key comment is that you have always talk fast or slow and that this is not a new finding meaning it occurred recently - so based on the timing your describing this is not likely do to a brain tumor.
Could someone die of. A malignant brain tumor? The answer is yes, of course. Do i think you have one? I do not believe so, especially if your speech issues are something you have "always" had, as you say. You may need a visit with a neurologist or speech specialist if it is a big problem but start by talking to your primary doc and let he/she guide you in this. Best to you.