Preheat oven to 375 degrees. Spray a 10 cup bundt pan with nonstick cooking spray.
Remove 2 Tablespoons of cake mix to a small bowl and reserve set aside.
In a large bowl beat together remaining cake mix, sour cream, oil, water, eggs, sugar, and vanilla, using a handheld electric mixer, for 2 minutes on high.
Mix together 2 tablespoons of reserved cake mix, brown sugar, cinnamon, and pecans; set aside.
Pour about 3/4 of batter into the prepared pan and then sprinkle cinnamon sugar mixture on the center of the batter. Spoon the remaining batter over the cinnamon sugar layer and spread evenly.
Bake 45-55 minutes in preheated oven. Cool for 25 minutes before removing from pan. Cool completely on a wire baking rack.
Glaze In a medium bowl, whisk powdered sugar and 2 tablespoons of milk until smooth. If necessary, add more milk, very slowly so it doesn’t get too thin, until desired consistency is achieved. Drizzle glaze over the cake. Sprinkle top with 2 Tablespoons chopped pecans and serve.