1. Trim fat from meat. Cut meat into 6 pieces. In a 3.5-4 quart crockery cooker, place meat, undrained tomatoes, onion, chipotle peppers, oregano, cumin, and garlic.
2. Cover and cook on low heat, setting for 8-10 hours or on high heat setting for 4-5 hours. Remove meat from cooker. Using two forks, pull meat apart into shreds. Place meat in a large bowl. Stir in cooking liquid to reach desired consistency. Divide meat among warm tortillas, spooning in just below the center. Top with cheese, pico de gallo salsa and if desired, sour cream. Roll up tortillas.
Note: To warm tortillas, wrap a stack in foil. Heat in a 350 degree F oven for 10 minutes to soften.
Pico de Galla Salsa: In bowl, combine 2 medium, finely chopped tomatoes; 2 T finely chopped onion; 2 T snipped fresh cilantro; 1 fresh serrano chili pepper, seeded and finely chopped; and dash sugar. Cover; chill several hours.