gingers famous chicken fettuccine alfredo

This is a big favorite in my house, hope you enjoy it!!

6 skinless, boneless chicken breast halves-cut into cubes
6 tablespoons butter, divided
4 cloves garlic, minced
1 tablespoon Italian seasoning
1 pound fettuccine pasta
1 onion, diced
1 (8 ounce) package sliced mushrooms
1/3 cup flour
1 tablespoon salt
3/4 teaspoon ground white pepper
3 cups milk
1 cup half and half
3/4 cup grated Parmesan cheese
8 ounces shredded Colby-Monterrey Jack cheese
3 Roma tomatoes, diced
1/2 cup sour cream

In a large skillet over medium heat combine chicken, 2 tablespoons butter, garlic and Italian seasoning. Cook until chicken is no longer pink inside. Set aside. melt 4 tablespoons butter in the skillet. Saute onion, 2 tablespoons garlic and mushrooms until the onions are transparent. Stir in flour, salt and pepper, cook 2 minutes. Slowly add milk and half and half, stir until smooth and creamy. Stir in Parmesan and Colby-Monterrey Jack cheeses, stir until cheese is melted. Stir in chicken mixture, tomatoes and sour cream.