In a stand mixer, beat together the cream cheese, mayonnaise, buttermilk and dressing mix. Add the Cheddar cheese and continue beating until thoroughly blended. Wrap the mixture in plastic wrap and place it in the freezer for 30 minutes. When firm, shape the wrapped cheese mixture into a log. Spread the pecans out on a baking sheet or a piece of wax paper. Unwrap the cheese log and roll it in the nuts to coat it on all sides. Serve with crackers or bagel chips.