In a medium mixing bowl, mix together until well blended the mayonnaise, sour cream, sugar, cilantro, red onion, garlic and jalapeno. Add salt and pepper to taste. Chill for at least 4 hours or as long as overnight to let flavors blend.
Very lightly toast the 8 slices of bread. Spread the sandwich spread mixture on one side of each toasted slice. On 4 slices of prepared bread layer the turkey, ham, jack cheese, Colby cheese, tomato slices, avocado slices and black olives. Top with remaining 4 slices of prepared bread.
Using a sharp serrated bread knife, cut each sandwich on diagonal from corner to corner. Make 2nd cut on opposite corner, making 4 sandwich segments. Secure segments with toothpicks and serve.