In a saucepan, combine the first 8 ingredients. Heat at medium heat just until a boil is reached. Put beef in large bowl and pour hot marinade over roast. Store, covered, in refrigerator for 24 to 72 hours. Turn roast twice daily. Remove roast from marinade and wipe dry with paper toweling. Reserve marinade. Melt butter in a pot on the stove and brown roast for 5 minutes per side. Add reserved marinade and bring liquid to a boil. Add contents of the pot to your crockpot. Simmer at setting 3 for approximately 3 hours. You may need to consult your crockpot directions for more accurate settings. Remove roast to hot platter and keep warm. Strain marinade liquid into a pot for the stove. Stir in crushed gingersnaps and sour cream. Heat until liquid just reaches a boil and gingersnaps are dissolved, about 12 to 15 minutes. While liquid is thickening, thinly slice roast. Pour hot gravy over sliced roast. Makes 8 to 10 servings.