Whisk together vegetable oil, vinegar, lime juice, cumin, chili powder, and garlic in a bowl and pour into a resealable plastic bag. Add the sliced beef, coat with the marinade, squeeze out excess air, and seal the bag. Marinate in the refrigerator for 4 hours or overnight.
Bring beef to room temperature, about 20 minutes.
Preheat oven to 350 degrees F (175 degrees C).
Transfer beef and lime juice marinade to a large baking dish. Add beef stock and cover baking dish with aluminum foil.
Bake in preheated oven until beef is very tender, about 2 1/2 hours. Allow meat to rest for 10 minutes before shredding with 2 forks. Drain and discard about 80% of liquid from meat and season with salt before serving.
