Place ribs in large shallow dish or resealable freezer plastic bag.
In small bowl, stir remaining ingredients with wire whisk. Reserve 3/4 cup sauce for dipping; cover and refrigerate. Pour remaining sauce over ribs. Cover dish or seal bag; refrigerate 8 hours, turning occasionally.
Spray 5- to 6-quart slow cooker with cooking spray. Remove ribs from marinade; discard marinade. Place 1 rack of ribs in bottom of slow cooker; stand remaining rib racks on their sides around edge of slow cooker. Cover; cook on High heat setting 1 hour. Reduce heat setting to Low; cook 5 hours longer.
In 1-cup microwavable measuring cup, microwave reserved 3/4 cup sauce uncovered on High 1 minute to 1 minute 30 seconds or, stirring once, until thoroughly heated. Serve sauce with ribs.