In a small bowl, mix 1 teaspoon dried thyme, ½ teaspoon onion powder, ½ teaspoon paprika, ½ teaspoon salt, and ½ teaspoon black pepper.
Pat 2 lbs pork tenderloin dry with paper towels and rub the seasoning evenly over all sides.
Pour ½ cup apple juice or chicken broth into the slow cooker. Place the pork inside.
Add 2 tablespoon butter and 4 smashed garlic cloves around the pork.
Cover and cook on LOW for 6 to 8 hours, until the pork is very tender.
In a saucepan, whisk together ½ cup water, 1 tablespoon cornstarch, ½ cup brown sugar, ¼ cup balsamic vinegar, 2 tablespoon soy sauce, and 1 tablespoon Dijon mustard.
Cook over medium heat, stirring often, for 3 to 4 minutes until thickened.
During the last hour of cooking, brush the glaze over the pork 2 to 3 times.
Optional: Transfer pork to a foil-lined baking sheet, brush with glaze, and broil 1 to 2 minutes until bubbly. Repeat glazing and broiling up to 3 times if desired.
Slice and serve with extra glaze spooned over the top.