Preheat your oven to 350°.

In a large bowl, combine the graham crackers, pecans, sugar and butter until the mixture is moist. Press into the bottom and edges of a non-stick 10 inch spring form pan. Bake 10 minutes at 350° and remove from oven.

In a large bowl, beat the cream cheese, sugar, flour and vanilla at medium speed until well blended. Add eggs, one at a time, mixing at low speed after each addition, just until blended. Blend in sour cream just until mixed. Reserve 1 1/2 c. cheesecake batter into a small bowl.

Add the pumpkin and pumpkin spice to the reserved cheesecake batter. Mix until smooth.

Spoon the pumpkin and cream cheese batters alternately over the crust. Cut through the batters with a butter knife several times to create a marble effect.

Add a pan of water to the lower rack in the oven. Place the cheesecake on the top rack and bake for 65 to 70 minutes at 350° or until the center is almost set. Allow to cook to room temperature. Run knife or metal spatula around edge of pan to loosen crust.

Refrigerate for at least 6 hours or overnight. Serve with whipped topping or whipped cream.