Preheat oven to 350°F. Prepare 13 in. x 9 in. baking pan with vegetable pan spray.
In medium bowl, whisk together flour, baking powder and salt.
For cake, beat brown sugar and butter with electric mixer in large bowl until light and fluffy. Add eggs, 1 at a time, beating well after each addition. Add vanilla; mix well. Add flour mixture alternately with sour cream in 3 additions. Spread mixture into prepared pan.
Bake 34 to 38 minutes or until a toothpick inserted into the center of the cake comes out clean. Cool completely in pan on cooling grid.
To prepare peaches, preheat grill or grill pan to medium-high heat. Grill peaches 3 to 4 minutes or until grill marks start to show. Let cool completely. Slice peaches 1/4 in. thick.
To prepare icing , beat cream cheese, sour cream, and vanilla with electric mixer in large bowl until smooth. Add confectioners' sugar, 1 cup at a time, beating until smooth. Beat in 3/4 cup toasted pecans. Spread icing on top of cooled cake. Just before serving, top with peaches and sprinkle with remaining 1/4 cup pecans.