Mix all the spices together in a small bowl. Remove 1/4 cup of the spices and set aside.
Remove pork from the packaging and pat dry with paper towels. Place pork on a large plate or platter and rub the remainder of the spices evenly over the meat.
In a 6-quart Crock-Pot, add 1-1/2 cups Dr. Pepper, 1 cup brown sugar, 1 cup red enchilada sauce, and 2 cups green enchilada sauce. Stir. Layer sliced onions along the bottom and sides of the Crock-Pot. Place spice-rubbed pork in the center with the fat cap up.
Cover Crock-Pot and cook on low for 7.5–9 hours, or high for 6–7 hours, until pork is tender and shreds easily. Low setting is recommended for best results; avoid overcooking to prevent dryness.
Add the remaining 1/4 cup spice mix, 1 cup Dr. Pepper, 1 cup brown sugar, all remaining enchilada sauce, both cans of diced chiles, undrained, and 2 tablespoons minced garlic to a blender. Blend thoroughly and refrigerate.
Once pork is tender, use tongs to transfer it to a large platter. Discard the bone and shred the meat, removing any fat. Optionally, use a slotted spoon to save the onions in a separate bowl. Remove 1 cup of liquid from the slow cooker and add it to a blender. Discard the remaining contents of the crockpot. Pour the blended mixture back into the Crock-Pot, add the shredded meat and onions if desired, and stir gently.
Cover and cook on low until warmed through, about 20–30 minutes. Season to taste with salt. Serve and enjoy!
Video
Notes
Note 1: To make a smaller batch that feeds about 7 people, use a 3–4-pound pork shoulder picnic roast instead, bone-in if you can find one. Halve all the other ingredients. Cook time will be about 1-1/2 hours shorter.Note 2: Use bone-in, if possible, as it adds great flavor and pulls out easily after cooking. Keep the fat cap—the white layer on top—facing up in the slow cooker. This way, as the pork cooks, the fat will render and enhance the flavor and tenderness. Once cooked, it can be easily discarded.Note 3: I’ve tested this recipe with Coke and Root Beer, but Dr. Pepper is the favorite. Be sure to use regular Dr. Pepper, not diet, as the sweetener in diet soda isn't heat-stable and won’t sweeten the pork properly while cooking.Note 4: Add sugar gradually to suit your taste. You can always add more if needed!Note 5: Enchilada sauce can vary significantly from brand to brand. I personally love and recommend Old El Paso® mild red and green enchilada sauce. If you can’t find this brand, taste the sauce first to ensure it’s not too spicy and that you enjoy the flavor, as it plays a big role in this recipe.Note 6: There’s a lot of fat to remove while shredding the pork. Set aside ample time for this. Tear it into large pieces, let it cool slightly, then shred by hand, discarding fat. Avoid overworking the pork—using a food processor or stand mixer can make it mushy.Storage: For leftovers, microwave individual portions of pork or warm all the leftover pork and sauce in a Crock-Pot on low for 1 hour. To freeze, fully cool the pork, then transfer it to airtight bags or containers, label them, and freeze for up to 3 months. Thaw overnight in the fridge and reheat in the slow cooker until warmed through.