Mix together Coca Cola and brown sugar for the marinade. Place in a large sealable plastic bag. Add pork loin, and massage to coat. Place in the fridge for 8 hours, to overnight.
Remove pork from marinade and place in slow cooker. Sprinkle pork evenly with garlic salt, onion salt, chili powder and cumin. Pour Coca Cola over pork. Cover and cook on low for 7-9 hours.
After the pork is tender, remove from slow cooker and use two forks to shred.
Pour out the liquid in the slow cooker.
Add pork back to slow cooker. In a blender or food processor combine all of the ingredients for the sauce. Pour over pork, stirring to coat.
Cook for an additional 20-30 minutes until heated through.