Begin the recipe by drying the pork roast. Rub generously with salt, ground black pepper, and brown sugar. Set aside.
Using a slow cooker, or the slow cooker setting on a pressure cooker (Instant Pot), Roughly chop 2 medium onions and add into the bottom of the slow cooker. Top with the seasoned pork roast.
Add the chipotle pepper in adobo sauce on top of the pork roast.
Slowly pour in the soda to cover everything in the slow cooker. Cover and allow to cook on high 4 hours or low, 6 to 8 hours depending on your slow cooker.
Carefully remove spicy soda pop pork from the slow cooker and shred using two forks. Serve on a bun while warm.