Heat oil in a skillet over medium-high heat and sear the pork shoulder on all sides (optional but enhances flavor).
Place the pork in the slow cooker and add the chopped onions and crushed garlic.
In a bowl, mix BBQ sauce, apple cider vinegar, chicken broth, brown sugar, mustard, Worcestershire sauce, chili powder, and thyme.
Pour the sauce mixture over the pork. Cover and cook on LOW for 8 hours or until the meat is tender and easily shredded.
Remove the pork from the slow cooker and shred it using two forks.
Return the shredded pork to the slow cooker and mix with the sauce for extra flavor.
Toast the hamburger buns with butter in a pan until golden brown.
Serve the pulled pork on buns with your favorite sides.