Prepare a slow cooker with nonstick cooking spray.

Cook the elbow macaroni according to package directions until al dente, boiling for about 6 minutes.

Meanwhile, in a medium skillet over medium-high heat, brown the ground beef, crumbling as it cooks.

Drain the ground beef well. Stir the taco seasoning into the ground beef.

In the slow cooker, add the cooked macaroni, seasoned ground beef, 2 cups fiesta blend cheese, tomatoes with green chiles, cream cheese, velveeta, sour cream, milk, salt, and black pepper.

Stir to evenly distribute the ingredients.

Cover the slow cooker and cook on low for 3 hours, stirring every hour.

Prior to serving, top with the remaining cheese. Re-cover until the cheese melts and serve.