Prepare cake mix according to package directions, and bake in 9 x 13 pan. Let cool for 10 minutes.
Using the handle of a wooden spoon, make small holes all over the surface of the cake. Pour 8 ounces of the caramel ice cream topping over the cake, spreading to cover. Let sit until cooled.
While the cake is cooling, beat the butter in a large bowl or the bowl of a stand mixer, until light and fluffy. Add the vanilla, cocoa powder, and powdered sugar, and mix until smooth. Add just enough milk to make a smooth, creamy frosting.
Spread the frosting over the cooled cake. Drizzle with the remaining caramel sauce, and sprinkle with the mini chocolate chips and pecans.