Cook the pasta in salted water per the package directions until al dente. Drain well.
In a medium mixing bowl, whisk together the mayonnaise, buttermilk, sugar, vinegar, onion and garlic powder, celery salt and black pepper.
Add the remaining ingredients, reserving the shredded cheese. Mix well. Taste and adjust the salt if needed.
Chill thoroughly add the shredded cheese after the salad has cooled.
Chill for at least 4 hours and stir well, before serving.