Slow Cooker Rocky Road Chocolate Cake

1 pkg. German chocolate cake mix
3.9 oz. pkg. chocolate instant pudding mix
3 large eggs, lightly beaten
1 C. sour cream
1/3 C. butter, melted
1 tsp. vanilla extract
3 1/4 C. milk, divided
3.4 oz. pkg. chocolate cook-and-serve pudding mix
1/2 C. chopped pecans
1 1/2 C. miniature marshmallows
1 C. semisweet chocolate chips
 vanilla ice cream, optional

Beat cake mix and next 5 ingredients, and 1 1/4 C. milk at medium speed with an electric mixer 2 min., scraping down sides of bowl as needed. Pour batter into a lightly greased 4 qt. slow cooker.
Cook remaining 2 C. milk in a heavy nonaluminum saucepan over medium heat, stirring often, 3-5 min. or just until bubbles appear (do not boil); remove from heat.
Sprinkle cook-and-serve pudding mix over batter. Slowly pour hot milk over pudding. Cover and cook on low 3 1/2 hrs.
Meanwhile, heat pecans in a small nonstick skillet over medium-low heat, stirring often, 3-5 min. or until lightly toasted and fragrant.
Turn off slow cooker. Sprinkle cake with pecans, marshmallows, and chocolate chips. Let stand 15 min. or until marshmallows are slightly melted. Spoon into dessert dishes, and serve with ice cream, if desired.