Preheat oven to 275 degrees.
Pat pork dry and season with salt and pepper.
In a bowl combine pineapple juice, cumin, oregano, achiote paste, guajillo chil pepper, chipotle, vinegar, minced garlic and lime juice. Set aside.
In a deep cast iron skillet or dutch oven, heat 2 tbsp oil over high heat. Once the oil is very hot, carefully sear pork on all sides. Remove from heat.
Pour pineapple juice mixture on top of pork and cover with lid or aluminum foil. Place in the oven for about 3 hours. The pork is ready when you can easily pull it apart with a fork.
Heat tortillas over open flame or over a hot skillet for a few seconds on each side. Repeat with all tortillas.
Serve with fresh pineapple avocado salsa, shredded jack cheese and hot sauce. Enjoy!