SPICES: Mix all the spices together in a small bowl. Remove 1/4 cup of the spices and add to a large blender and set aside for now.
PREP PORK: Remove pork from the packaging and pat dry all over with paper towels. Place pork on a large plate or platter and take the remainder of the spices and rub evenly all over the meat.
CROCKPOT: To a 6-quart or larger crockpot add the following: 1-1/2 cups (350g) Dr. Pepper, 1 cup (200g) packed brown sugar, 1 cup (240g) red enchilada sauce, and 2 cups (470g) green enchilada sauce. Stir together. Add 2 thinly sliced onions -- cover the bottom of the slow cooker with the onions and press them up around the sides of the crockpot. Add spice-rubbed pork to the center of the crockpot, making sure the fat cap is facing up.
COOK: Cover crockpot and cook on low for 7.5-9 hours or high for 6-7 hours or until pork shreds easily and is tender. I recommend using the low setting for the best results. (Fairly forgiving meat, but don't cook too long or it will taste dry.)
BLENDER SAUCE: Once the pork is in pan, finish the blender sauce: To the 1/4 cup seasonings, add 1 cup (230g) Dr. Pepper and 1 cup (200g) brown sugar. Add all the remaining enchilada sauce from the cans (a scant 1-1/2 cups red and scant 1/2 cup green). Add both cans of diced chiles (undrained) and 2 tbsp minced garlic. Blend and place in the fridge.
SHRED: Once pork is fork tender, remove with tongs to a large platter or bowl with sides. Pull out the bone and discard. Shred the meat, discarding all the fat as you shred (Note 8). If you'd like to save the onions, use a slotted spoon to pull them out and place in a separate bowl. (Otherwise, skip and discard onions). Once the pan is empty of pork and onions, pull out 1 cup (140g) of the liquid left in the slow cooker and add to the blender with the other ingredients. Blend once more. Discard the rest of everything in the crockpot. Pour the contents of the blender into the crockpot. Return the shredded meat (and onions if using) and stir gently. Cover and cook on low until warmed through, about 20-30 minutes. Season to taste; I typically add another 1/2 up to 1 tsp salt. Serve and enjoy!