Preheat the oven to 350°F. In a large bowl, add the cake mix, pudding mix, oil, eggs, water, and sour cream until well combined.
Gently stir in the pistachios (leaving some back to sprinkle on top) In a separate small bowl, stir together the sugar and cinnamon.
Grease two regular-size loaf pans (9X5) and sprinkle the sugar mixture evenly on the bottom and sides.
Pour half the batter into each pan, smoothing the top. Sprinkle remaining pistachios on top.
Bake for about 45 minutes or until a toothpick inserted in the center comes out clean. Let the loaves cool completely before adding the glaze.
To make the glaze, whisk together powdered sugar and vanilla. Add milk one tablespoon at a time until you reach the desired consistency. Drizzle over the cooled bread.