Heat oven to 375°F. Beat flour, 3/4 cup butter, 1/2 cup sugar, the cocoa and 1 teaspoon vanilla in large bowl with electric mixer on low speed until crumbly. Press in bottom of ungreased 15x10x1-inch pan. Bake 20 minutes.
Meanwhile, beat eggs, 1/2 cup sugar, 3 tablespoons butter, the corn syrup and 1/2 teaspoon vanilla in medium bowl with wire whisk until smooth. Stir in pecans and chocolate chips. Spoon evenly over baked crust.
Bake about 15 minutes or until set. Cool completely, about 1 hour. For bars, cut into 8 rows by 4 rows.