Stir in the gochujang, sugar, soy sauce and rice vinegar.
Cover the slow cooker, turn on HIGH and cook for two hours.
Turn down the heat to LOW and cook for another five hours.
About an hour before the cooking time is up, taste the cooking liquid and adjust the seasonings. You may want to add more soy sauce (or salt to prevent the stew from turning too dark) or sugar, or both.