Preheat oven to 350. Mix the graham crackers, butter, and 1/4 cup brown sugar together. Press into a lightly greased 9 by 13-inch pan. Bake for 10 minutes, and place in the refrigerator to thoroughly cool. Using a mixer, beat cream cheese until very smooth. Add pumpkin, 2 tsp. vanilla, 3/4 cup granulated sugar, cinnamon, and pumpkin pie spice. Beat until completely smooth, and set aside.In a separate bowl, beat heavy cream just till it starts to thicken. Add 1/2 cup granulated sugar, 1/4 cup brown sugar, and 1 tsp. vanilla. Continue beating until cream is stiff but still spreadable.Measure out 2 cups of the whipped cream mixture and fold it into the pumpkin mixture until incorporated. Spread this onto the graham cracker crust, and top with remaining whipped cream mixture. Refrigerate at least 4 hours before serving.