Pumpkin Fudge

Ok, I was revising the original recipe so I made it 3 times trying to get it to set up. the 2nd batch did set up. It is VERY important to cook the sugar mixture long enough. But after this fudge set out for a while it became a gooey mess. So...I think the recipe still needs a little work. If you play with this and get a good recipe that doesn't require 3 cups of sugar be sure to let me know!
regardless of it not setting up---it was delicious!

Pumpkin Fudge
2/3 cups white sugar
1 TB light margarine
¼ tsp cream of tartar
1/2 cup canned pumpkin
1 teaspoon pumpkin pie spice
2 cups butterscotch chips
1 (7 ounce) jar marshmallow creme
1 C. Splenda
1 teaspoon vanilla extract

Spray 11x7 pan with cooking spray. In a heavy saucepan, combine sugar, margarine, cream of tartar, pumpkin, and spice; bring to a boil, stirring constantly. Continue boiling over medium heat until mixture reaches 234 degrees F (118 degrees C) on a candy thermometer, about 10 minutes. (ahhh...I boiled 4-5 minutes...maybe a little longer would do the trick)
Remove from heat. Stir in butterscotch chips. When chips are melted, add marshmallow cream, and vanilla. Mix until well blended.
Immediately pour butterscotch mixture into prepared pan. Spread evenly. Cool at room temperature. Cut into squares, and store in the refrigerator in an air-tight container.
Yield: 24 small squares. Per square= 108 Calories; 1g Fat (6.2% calories from fat); trace Protein; 26g Carbohydrate; trace Dietary Fiber; 1mg Cholesterol; 16mg Sodium. Exchanges: 0 Grain(Starch); 0 Vegetable; 0 Fruit; 0 Fat; 1 1/2 Other Carbohydrates.