Bring a large pot of salted water to a boil. Cook pasta according to package directions until al dente. Drain and rinse under cold water until cool. Set aside.
In a large bowl, whisk together mayonnaise, sour cream, ranch seasoning mix, and milk until smooth and well combined.
Add the cooled pasta, cherry tomatoes, cucumber, red bell pepper, cheddar cheese, and parsley to the bowl. Stir gently until everything is evenly coated with dressing.
Season with salt and pepper to taste. Cover and refrigerate for at least 30 minutes before serving to allow flavors to meld. Stir again before serving.