In a food processor, combine the mayo, sour cream, chipotle peppers, dill, parsley, chives, garlic powder, onion powder, salt, pepper, and sugar. Blend until smooth.
Add the milk and lime juice to adjust the thickness. For a pourable dressing, add more milk, for a thicker dip, use less. Blend again to combine. Taste the dressing and adjust the seasonings, as desired.
Pour into a jar and chill in the refrigerator until ready to serve. This dressing will keep nicely in the refrigerator for up to a week.