Bring a large pot of generously salted water to a rolling boil. Add the rotini and cook according to package directions until al dente, usually 8 to 10 minutes.
Drain the pasta in a colander and rinse under cold running water until fully cooled. Shake off excess water and let it drain completely.
Transfer the cooled pasta to a large mixing bowl. Pour the reserved pickle juice over the pasta and toss well. Let it sit for 10 minutes while you prep the rest of the ingredients.
In a small mixing bowl, whisk together the mayonnaise, sour cream, Dijon mustard, and garlic powder until completely smooth. Season with a pinch of salt and black pepper.
Chop the dill pickles, red onion, celery, and fresh dill into small, even pieces. Cube or shred the sharp cheddar cheese.
Add the chopped pickles, red onion, celery, fresh dill, and cheddar cheese to the bowl with the marinated pasta. Pour the dressing over the top.
Fold everything together with a large spoon or spatula until evenly coated. Taste and adjust salt and pepper if needed.
Cover the bowl tightly or transfer to an airtight container. Refrigerate for at least 1 hour to let the flavors settle.
Give it one more stir before serving, since the dressing can settle toward the bottom while chilling. Serve cold, straight from the fridge.