Make Graham Cracker Crust: In a medium bowl, with fork, lightly toss crumbs with butter, to mix well. With back of metal spoon, press to bottom and sides (not rim) of 9-inch pie plate. Refrigerate.
Preheat oven to 350°.
Make Pumpkin Cheese Filling: In a large bowl of electric mixer, combine cheese, ¾ cup sugar, flour, peels, ¼ teaspoon vanilla, eggs, egg yolks, and pumpkin; beat at medium speed until smooth.
Turn into crust. Bake 35-45 minutes, or until center of pie seems firm when pie is gently shaken.
Meanwhile, make Sour Cream Topping: In small bowl, combine sour cream with sugar and vanilla; mix well.
Spread topping evenly over pie. Bake 10 minutes longer.
Let pie cool completely on wire rack - about 1 hour.
Refrigerate, overnight.