Cook the pasta according to its package directions. Drain the pasta and let it cool for at least 5 minutes.In the meantime, prepare the dressing. In a large bowl, add the mayonnaise, sour cream, sugar, vinegar, salt, and pepper. Whisk until well combined and sugar is dissolved.Add the pasta to the dressing and stir to evenly coat the pasta. Add the broccoli, onion, carrots, grapes, and bacon bits. Stir until well combined.Cover and refrigerate for at least 1 hour before serving.