In a large bowl, combine the first 6 ingredients; add 1-1/4 cups milk. Beat on low speed 30 seconds. Beat on medium 2 minutes. Transfer to a greased 4- or 5-qt. slow cooker. Sprinkle cook-and-serve pudding mix over batter., In a small saucepan, heat remaining milk until bubbles form around sides of pan; gradually pour over contents of slow cooker., Cook, covered, on high 3-4 hours or until a toothpick inserted in cake portion comes out with moist crumbs., Turn off slow cooker. Sprinkle marshmallows, chocolate chips and pecans over cake; let stand, covered, until marshmallows begin to melt, about 5 minutes. Serve warm. If desired, serve with ice cream.