Whisk the beef broth, tomato paste, maple syrup, molasses, vinegar, Worcestershire sauce, mustard and chili powder in a 4-quart slow cooker. Add the leek and set the pork on top; nestle the thyme sprigs in the liquid. Add the black-eyed peas. Cover and cook on low until the pork is fork-tender, 7 to 8 hours, or on high, 4 hours.
Remove the pork to a cutting board and slice. Add up to 1 cup water to the beans in the slow cooker to loosen; serve with the pork. Top with thyme.