In the latter, a person has difficulties framing his thoughts—so stuttering
is possible. It can be the result of a visual processing disorder.
Also if stuttering developed in adulthood, it can be due to anxiety, head injury, tumor, stroke or drug use. All these may affect speech and learning, and visual perception of letter.
You need to consult a speech and language therapist to assess the cause of your problem. Do request your PCP to refer you to one. Take care!