Brush inside of 3 1/2 or 4-quart slow cooker with oil or spray with nonstick cooking spray. In large skillet, brown ground beef sirloin with onion and garlic over medium-high heat for 8 to 10 minutes or until thoroughly cooked, stirring frequently. Drain. Stir in taco seasoning mix, salt and pepper.
Place 3 tortillas in bottom of oiled slow cooker. Top with beef mixture, broth, tomato sauce and enchilada sauce. Sprinkle with 1/2 cup of the cheese. Layer 3 more tortillas. Top with beans, corn, green chiles, half of the olives and 1/2 cup cheese.
Top with remaining 3 tortillas. Sprinkle with remaining 1/2 cup cheese and olives. Cook on high setting for 2 1/2 to 3 hours or on low setting for 6 to 7 hours. Uncover slow cooker for last 30 minutes of cooking time. Top individual servings with sour cream.