Place chicken in slow cooker bottom; sprinkle evenly with taco seasoning and add 1/4 cup water.
Cover; cook on low 3-4 hours or high 2 hours until cooked through and easily shredded with fork.
Remove chicken; shred with two forks and return.
Add Velveeta, tomatoes with chiles, cream cheese, cheddar, jalapeños, sour cream, and milk.
Stir; cover and cook on low another 1 hour, stirring every 20 minutes, until cheeses melt and dip is smooth and creamy.
Serve hot with chips and optional extra jalapeños, green onions, or cilantro.