Different messages need different voices:

• Urgency — faster pace, higher energy, short sentences
• Trust — slower pace, lower pitch, warm and steady
• Inspiration — rising energy and a powerful pause before the ask
• Bad news — even volume, lower pitch, calm and honest

This is not acting. It is letting your real feeling about the message reach your voice instead of burying it under a default "professional" monotone. Your instincts already know the right tone. The skill is getting out of their way.