Heat oven to 350°F (325°F for dark or nonstick pan). Place paper baking cups in each of 24 regular-size muffin cups.
In a heavy 8-inch nonstick skillet, cook pecans and 2 tablespoons of the sugar over low heat for about 8 minutes, stirring constantly, until the sugar is melted. Spoon and spread pecans onto a sheet of waxed paper. Sprinkle with the remaining 1 tablespoon sugar and toss to mix.
In a large bowl, beat cake mix, pumpkin, water, oil, eggs, and pumpkin pie spice with an electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping the bowl occasionally. Divide batter evenly among muffin cups (about two-thirds full).
Bake 19 to 24 minutes or until a toothpick inserted in the center comes out clean. Cool in pans 10 minutes; remove from pans to a cooling rack. Cool completely, about 30 minutes.
Frost cupcakes with the frosting. Roll the edge of the frosted cupcakes in the pecans; press lightly into the frosting. Store loosely covered.
