Bring the sugar, water, and Jell-O to a boil in a large saucepan; boil for 3 minutes.
Stir in the pineapple, lemon, and orange juice.
Pour the mixture into a large, freezable container and freeze. (This is best done the day before serving but will keep in the freezer for weeks.)
When ready to serve, remove the container from the freezer 15-20 minutes ahead of time. Break up the frozen slush with a fork, and then combine the contents of the container with the carbonated beverage in a punch bowl. Stir until slushy and enjoy!