In a dry large skillet toast ancho peppers on both sides about 2 minutes or until they crackle and just turn color, turning once halfway through cooking. (Be careful not to burn them; it will make the mole bitter.) Place ancho peppers in a small bowl; cover with boiling water and let stand for 30 minutes to rehydrate. Drain peppers, discarding water. Remove seeds from ancho peppers; set aside.
In the same large skillet cook onion and garlic in hot oil over medium heat about 5 minutes or until onion is tender. Stir in sunflower kernels, cinnamon, cumin seeds, and allspice; cook and stir for 3 to 4 minutes more or until mixture is very fragrant. Transfer mixture to a blender or food processor.
Add 1-1/2 cups of the chicken broth, the bread, tomato, chipotle peppers, and ancho peppers to the blender or food processor. Cover and blend or process until smooth, adding more of the chicken broth if needed to thin the mixture.
Transfer mixture to a large saucepan. Stir in the remaining broth, the chocolate, and the 2 teaspoons sugar. Bring to boiling; reduce heat. Simmer, uncovered, about 30 minutes or until desired consistency. Season to taste with salt, black pepper, and additional sugar. Cover to keep warm.
Meanwhile, season meat with salt and black pepper. For a charcoal grill, arrange hot coals around a drip pan. Test for medium-high heat above pan. Place meat on grill rack over pan. Cover and grill for 30 to 35 minutes or until internal temperature registers 155 degrees F on an instant-read thermometer. (For a gas grill, preheat grill. Reduce heat to medium-high. Adjust for indirect cooking. Grill as above.) Remove meat from grill. Cover with foil and let stand for 15 minutes. The temperature of the meat after standing should be 160 degrees F. Slice into 1/2-inch slices.
Place meat slices on a serving platter. Top with mole sauce and sprinkle with pumpkin seeds.