Heat the oven to 350 degrees. Place the pork in a 4 quart Dutch oven.
Combine the tomatoes, onion, apple juice, lime juice, garlic, chili powder and salt in a medium bowl. Pour the mixture over the pork and cover. Bake the roast for 3 to 3 1/2 hours or until the pork is very tender.
Remove the pork from the pan and cool slightly. Remove any fat or bones and shred the pork with a fork. Strain the pan juices and return the tomatoes and onions to the Dutch oven.
Add the pork to the sauce and mix well. Skim the fat from the pan juices. If the pork is dry, moisten with a little additional juice.
Wrap the tortillas in aluminum foil and heat for about 15 minutes or until warm. Place 1/4 cup meat on each tortilla.
Top each taco with avocado slices, tomatillo salsa and a dollop of sour cream.