The night before you want to cook the carnitas, place pork chunks in a large bowl. Then cover the pork with Dr. Pepper. (I usually use about 1 liter for this.) Cover the bowl in plastic wrap or foil and allow it to sit overnight in the fridge.
In the morning, drain the Dr. Pepper from the bowl.
In a small bowl, mix together the cumin, salt, pepper, and chili powder. Rub half of the spice mixture all over the pork.
Add the onions and bay leaves to the bottom of the slow cooker.
Place a large skillet over medium-high heat and pour in the oil. Once the oil is hot, sear the pork chunks on all sides for 3 minutes until browned. (You may need to work in batches.) Remove the pork and place it in the slow cooker.
Pour 1/4 cup of orange juice into the hot skillet that cooked the pork, and scrape up the browned bits on the bottom of the pan. Then pour the juice into the slow cooker.
Add garlic, the rest of the spice mixture, the remaining 1/4 cup of orange juice, and 1 cup of Dr. Pepper into the slow cooker
Cover and cook on LOW for 6-8 hours, until meat is tender and falling apart.
Line a baking sheet with foil and preheat your oven to broil on HIGH.
Shred the meat and place it in a single layer on the baking sheet. Place under the broiler for 4-5 minutes
Flip the meat over and drizzle with 2/3 cup of the cooking liquid in the slow cooker. (It's okay if some onions get added, just make sure to discard the bay leaves.)
Place back under the broiler for another 3-5 minutes until crispy. Remove from oven and drizzle with another 2/3 cup of the cooking liquid.
If serving from the baking sheet or a serving bowl, you can sprinkle the carnitas with some chopped cilantro for garnish.
If making tacos, warm up the tortillas. Then add about 3 ounces of carnitas (1/3 cup) to a tortilla, and top with red cabbage slaw and jalapenos. Serve immediately.