
In a 6 to 8-quart slow-cooker, stir together the macaroni, whole milk, evaporated milk, heavy cream, butter, salt, pepper, paprika, and cayenne.
Cover and cook on high for 30 minutes. Stir the mixture, cover, and cook until the noodles are almost tender, about 25 minutes more. (Check the noodles—if they are still too firm, continue to cook in 10 minute increments until they are tender, with a slight bite.)
With the slow cooker still on high heat, add the American cheese, gently folding it into the macaroni with a rubber spatula until almost melted. Working in three batches, gently fold in the cheddar and gouda, making sure the cheese is fully melted before adding the next batch.
Serve immediately, or set the slow cooker to warm for up to 2 hours. (When holding the mac and cheese on warm for serving, gently stir occasionally and fold in 2 tablespoons of warm milk, as needed, to loosen the sauce.)