Lightly grease the inside of the slow cooker with butter or non-stick spray.
In a medium bowl, whisk together the melted butter and flour until smooth to create a roux.
Pour the whole milk and heavy cream into the slow cooker, then whisk in the roux mixture until fully combined.
Add garlic powder, onion powder, smoked paprika, salt, and black pepper to the slow cooker and stir to combine.
Add the uncooked elbow macaroni and shredded chicken to the slow cooker and stir to combine.
Cover and cook on low for 3 hours, stirring halfway through the cooking time to prevent pasta from sticking.
After 3 hours, stir in the shredded cheddar cheese and mozzarella cheese until melted and creamy.
Sprinkle the grated Parmesan cheese on top, cover, and cook for an additional 15-30 minutes on low until cheese is melted and bubbly.
Give the mac and cheese a final stir, then serve hot.