The short breath is because your muscles are tight and are not letting enough air through. You need to breathe from your abdomen like a singer. Speech therapy will help a lot. Lee Silverman Voice Therapy is specifically for PWP. Even though the emphasis of LSVT is for helping a quiet voice, it helps all speech problems in PWP.

Exercise is at least as important if not more important than taking meds in PD. LSVT will show you how to exercise the muscles used for speech.