In a medium bowl mix brown sugar, chili powder, and pepper. Rub mixture over the pork.
Turn on electric pressure cooker to BROWN setting. Add a splash of oil. When pot will get hot add the pork and brown on all sides, about 5 minutes. Turn off the pressure cooker, remove the pork to a plate.
Add chicken stock and vinegar into the drippings in the pot. Mix well. Add the pork back. Add sliced onion and crushed garlic. Set lid valve to steam and lock the lid. Programm electric pressure cooker to cook on low for 8-10 hours.
Make coleslaw the last in a medium bowl mix with whisk mayonnaise, vinegar, brown sugar, and salt. Pour over coleslaw mix. Cover and refrigerate for 30 minutes.
After the cooking cycle is complete, careful release remaining steam by an opening lid. Transfer pork to a large baking sheet.
Switch electric pressure cooker to the SAUTE mode and simmer liquid until reduced by half, about 15 minutes. Keep removing any fat that rises to the top — season to taste.
Use two forks or shredder claws to shred the pork into small chunks.
In a large bowl, mix shredded pork and 3 cups of liquid.
Serve in hamburger buns with barbecue sauce and coleslaw.