Preheat your oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
In a large mixing bowl, cream the softened butter and granulated sugar together until light and fluffy, about 3-4 minutes.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Gradually add the dry ingredients to the wet mixture, alternating with the sour cream. Begin and end with the flour mixture. Mix until just combined.
Gently fold in the diced peaches and cinnamon until evenly distributed.
Pour the batter into the prepared baking pan and spread it evenly.
Bake for 40-45 minutes, or until a toothpick inserted in the center comes out clean.
Allow the cake to cool in the pan for about 15 minutes before transferring it to a wire rack to cool completely.