Add the pasta and milk. Pour the whole milk and evaporated milk into the crockpot. Add the salt and uncooked elbow macaroni, then stir to combine. Cover and cook on HIGH.
Stir after 1 hour. Remove the lid and stir the macaroni, separating any noodles that have stuck together. Cover and continue cooking.
Add the cheeses after 1½ hours. Stir the macaroni again, then add the cubed Velveeta and sharp cheddar. Stir to distribute the cheese, cover, and continue cooking on HIGH for another 30 minutes.
Finish melting the cheese. After 2 hours of cooking, stir again and add the black pepper. Taste carefully and adjust the salt as needed. Switch the crockpot to WARM for another 30 minutes to allow any remaining pieces of cheese to melt.
Stir and serve. Stir until the melted cheese coats the macaroni. If the sauce has become too thick, add a little milk and stir until it reaches your preferred consistency. Serve warm.