Place chicken breasts in the bottom of your slow cooker and sprinkle the taco seasoning evenly over them, then add 1/4 cup water.
Cover and cook on low for 3-4 hours or on high for 2 hours, until the chicken is cooked through and shreds easily with a fork.
Remove the chicken and shred it with two forks, then return it to the slow cooker.
Add the Velveeta cubes, diced tomatoes with chiles, cream cheese, cheddar cheese, jalapeños, sour cream, and milk to the slow cooker with the shredded chicken.
Stir everything together, cover, and cook on low for 1 additional hour, stirring every 20 minutes, until all the cheese is melted and the dip is smooth and creamy.
Serve hot with tortilla chips and optional toppings like extra jalapeños, green onions, or cilantro.