Preheat oven to 350 degrees F. Coat a 9- x 13-inch baking dish with cooking spray. In a large bowl with an electric mixer on low speed, beat cake mix, pudding mix, eggs, and oil until blended. Gradually add 1-1/4 cups cola.
Increase mixer speed to medium and beat 2 minutes; pour batter into prepared baking dish. Bake 30 to 35 minutes, or until a toothpick inserted in center comes out clean. Cool in pan on a wire rack 10 minutes.
In a large saucepan, combine butter, cocoa, and remaining cola. Cook over medium heat until butter melts, stirring constantly. Do not allow to boil. Remove from heat. Stir in confectioners' sugar and vanilla, then the pecans. Spread warm frosting over top of warm cake. Cool completely on a wire rack. This cake is also great made with cherry-flavored cola!