Shred the cheese using the medium holes on a box grater. This step is important. Do not use pre-shredded cheese. Shredding your own makes a world of difference.
In a large bowl combine the cream cheese and mayonnaise and mix well.
Add the pimientos, BBQ rub, mustard powder and onion powder. Mix well. Gently stir in the cheese.
Pile high on toasted bread for the best pimiento cheese sandwiches ever!