Grab a slow cooker and put the onions in the bottom. Next, place the pork in the slow cooker on top of onions and salt and pepper to your taste. Pour the can or bottle of Dr Pepper over the meat. Put the lid on and cook on low for 6-8 hours until meat is fork-tender and easy to shred with two forks. Serve with your favorite barbecue sauce on French Bread Rolls with coleslaw, if desired.