(a) A person is incompetent to stand trial if the person does not have:
(1) sufficient present ability to consult with the person's lawyer with a reasonable degree of rational understanding; or
(2) a rational as well as factual understanding of the proceedings against the person.
(b) A defendant is presumed competent to stand trial and shall be found competent to stand trial unless proved incompetent by a preponderance of the evidence.