Slow Cooker BBQ Pulled Pork

Name: Slow Cooker BBQ Pulled Pork
Ingredients: 2 Tbsp. Diamond Crystal or 1 Tbsp. plus ½ tsp. Morton kosher salt, plus more; 1 Tbsp. chipotle or other red chile powder; 1 Tbsp. freshly ground black pepper; 1 Tbsp. garlic powder; 2 tsp. dry mustard; 2 tsp. ground coriander; 1 tsp. ground cumin; 1 3–4-lb. boneless pork shoulder (Boston butt), excess fat trimmed; 2 Tbsp. vegetable oil; 1 large onion, quartered; 10 garlic cloves, smashed; 1 12-oz. can cola or other dark soda (such as root beer or Dr. Pepper); ½ cup (or more) barbecue sauce; Warmed hamburger buns, coleslaw, bread-and-butter pickle slices, and hot sauce (for serving); A 6–8-qt. slow cooker