Preheat oven to 350°F.
Bring large pot of salted water to boil. Add pasta and cook according to package directions until al dente. Drain and set aside.
Heat large pot over medium-low heat. Add 3 tablespoons butter, olive oil, onion, garlic salt, salt and pepper. Cook 20-30 minutes, stirring occasionally until onions are golden brown in color and caramelized. Increase heat to medium and stir in flour and remaining butter. Whisk constantly for 2-3 minutes to create a roux.
Add milk and barbeque sauce, whisking constantly, cook 5 minutes until slightly thickened. Reduce heat to medium-low. Add shredded cheese. Continue to stir until sauce is creamy and cheese has melted. Stir in pasta, followed by pulled pork. Transfer mac and cheese to oven safe baking dish and sprinkle with Texas toast crumbles. Bake 15 minutes or until light golden brown.
To reheat, add a few tablespoons of milk, stir and warm.