I would experiment with reducing the amount of ice cream and adding ice cubes to the mixture.
You might also try eliminating the ice cream and using a combination of heavy cream and ice cubes.
Finally I would look at recipes for frozen cocktails as opposed to milkshakes that contain alcohol.
Frozen Mudslide
Ingredients
4 cups crushed ice
2 (1.5 fluid ounce) jiggers vodka
2 (1.5 fluid ounce) jiggers coffee-flavored liqueur
2 (1.5 fluid ounce) jiggers Irish cream liqueur
2 tablespoons chocolate syrup
1/2 cup whipped cream
Directions
In a blender, combine crushed ice, vodka, coffee liqueur, and Irish cream liqueur. Drizzle in Chocolate syrup. Blend until smooth. Pour into glasses and garnish with whipped cream.
Good luck and remember practice, practice, practice!