Slice onion and spread it in the bottom of the slow cooker. Smash and chop garlic cloves and spread it in the bottom of the slow cooker as well.
Place pork shoulder over garlic and onions.
Mix brown sugar, chili powder, cumin, and salt together. Rub pork with this mixture all over the top and the sides.
Pour chicken stock around pork shoulder.
Squeeze the lime juice around the meat and over it.
Cover and cook on LOW for 8-10 hours.
Once the pork is cooked, take out the large bones and the excess fat.
Scoop out excess broth and set it aside. (You can keep it in a glass jar and use it in stewing potatoes, soup, gravy, or sauce.) Leave a little bit of broth with pork to keep it moist.
Start pulling apart all the meat, feeling around for small bones. I like to take out all the fat while pulling the pork too but you can choose to leave it in or take it out as well.
Once all the meat is pulled, mix it and taste to see if you need to find a little more salt or chili powder.
For tacos:
Add about 1/3-1/2 cup of pulled pork to taco shells and top it off with coleslaw and some cashews, if you wish. You can also add jalapenos, avocado, or red onions.