Prepare the Crockpot: Lightly grease the inside of a 4-quart (or larger) slow cooker with cooking spray to prevent sticking and make cleanup easier.

Combine the Base: Add the cubed cream cheese, Ranch dressing, Buffalo-style hot sauce, garlic powder, and black pepper directly into the prepared slow cooker.

Start Melting: Cover the slow cooker and set the temperature to LOW. Cook for 30 to 45 minutes, stirring occasionally until the cream cheese is completely melted and the sauce is smooth and uniform.

Add the Chicken and Initial Cheese: Once the base is smooth, stir in the 3 cups of shredded cooked chicken. Mix thoroughly until the chicken is completely coated in the creamy buffalo sauce. Then, stir in 1 1/2 cups of the shredded Monterey Jack cheese and 3/4 cup of the shredded cheddar cheese, reserving the remaining cheese for the top layer.

Continue Cooking: Cover the slow cooker again and continue cooking on LOW for another 45 minutes to 1 hour, or until the dip is hot, bubbly around the edges, and the cheese has fully melted into the mixture. Stir the dip halfway through this cooking time to ensure even heating and prevent scorching on the bottom.

Final Cheese Layer: Once the dip is heated through, sprinkle the remaining 1/2 cup of Monterey Jack and 1/4 cup of cheddar cheese evenly over the top layer of the dip.

Melt the Top: Replace the lid and continue cooking for 10 to 15 minutes, or until the cheese topping is completely melted and bubbly.

Serve and Garnish: Switch the slow cooker setting to KEEP WARM for serving. Garnish the dip with chopped green onions and/or extra blue cheese crumbles, if desired. Serve hot directly from the crockpot with sturdy tortilla chips, celery, and carrot sticks.