Bring a large pot of salted water to a boil. Cook rotini pasta according to package instructions until al dente, about 8-10 minutes. Drain and rinse with cold water.

In a skillet, cook the bacon over medium heat until crispy, about 5-7 minutes. Transfer to a paper towel to cool, then crumble into pieces.

In a medium bowl, mix together mayonnaise, sour cream, and milk until smooth. Adjust consistency as desired.

In a large bowl, combine the pasta, bacon, and diced tomatoes. Pour the dressing over and toss until coated.

Fold in the chopped lettuce just before serving to keep it fresh.

Cover and chill in the refrigerator for about 20-30 minutes before serving.