Combine streusel ingredients in a small bowl. Mix until mixture is crumbly. Set aside.
Combine flour, pumpkin pie spice, cinnamon, baking soda, baking powder, and salt in a bowl. Beat sugar and butter in mixing bowl until light and fluffy.
Add eggs, one at a time, beating well after each one. Add pumpkin, sour cream and vanilla, and mix well. Gradually beat in flour mixture.
Spoon half of batter into pan. Sprinkle streusel over batter, keeping it in the middle of the pan (don't allow it to touch sides). Top with remaining batter. Make sure batter layer touches edges of pan.
Bake for 50-60 minutes or until toothpick comes out of middle of cake clean. Cool for 30 minutes in pan on wire rack. Invert onto rack to cool completely.