Preheat oven to 350°F. Place 2 cups of the pecan pieces in food processor or blender; cover. Process until finely ground, using pulsing action. Mix with granulated sugar and butter. Press firmly onto bottom and up side of 9-inch pie plate. Bake 12 to 15 minutes or until lightly browned. Cool completely. (If crust puffs up during baking, gently press down with back of spoon.)
Microwave caramels and 1/3 cup of the whipping cream in microwaveable bowl on high 2-1/2 to 3 minutes or until caramels are completely melted, stirring after each minute. Pour into crust. Chop remaining cup pecans; sprinkle over pie.
Place chocolate, remaining 1/3 cup whipping cream, the powdered sugar and vanilla in saucepan; cook on low heat just until chocolate is completely melted, stirring constantly. Pour over pie; gently spread to evenly cover top of pie.
Refrigerate at least 2 hours. Store leftover pie in refrigerator.