Peel shrimp; devein, if desired. Thread shrimp onto skewers.
Preheat grill to 350° to 400° (medium-high). Combine Southwest seasoning and garlic in a long shallow dish; add lime juice, lemon juice, and shrimp, turning to coat. Cover and chill 10 minutes. Remove shrimp from marinade, discarding marinade.
Grill shrimp, without grill lid, 2 to 3 minutes on each side or just until shrimp turn pink. Remove shrimp from skewers. Serve in warm tortillas with next 4 ingredients. Garnish, if desired.
Note: For testing purposes only, we used Emeril's Southwest Seasoning.
Southwest Cream Sauce: Whisk together 1 (16-oz.) container sour cream; 1 garlic clove, minced; 2 Tbsp. finely chopped red onion; 1 tsp. chili powder; 1/2 tsp. ground cumin; 1/2 tsp. ground red pepper; and 1/4 tsp. salt. Whisk in 2 Tbsp. chopped fresh cilantro and 2 Tbsp. fresh lime juice until smooth. Cover and chill until ready to serve. Makes about 2 cups; Prep: 10 min.
Soak wooden skewers in water at least 30 minutes before grilling to keep them from burning.