Combine all of the ingredients in a crockpot. Let cook on low for 8 hours. Proceed with canning instructions below or refrigerate in jars for up to 30 days.
Alternative method
If using fresh pumpkin, mix with sugar, lemon, ginger, cinnamon and allspice in a large bowl. Let stand at room temperature 8 to 10 hours
Transfer to a heavy saucepan, add 1/2 cup water and bring to a boil. Simmer on low heat, stirring often, for 40 to 60 minutes, to desired consistency. (With canned pumpkin, mix ingredients in heavy saucepan; bring to a boil and simmer on low about 20 minutes, to thicken.)
Refrigerate or freeze, see link below in Ben's comment. Revised this recipe to remove the canning instructions 9/9/14