Macaroni Casserole

1 14oz package deluxe macaroni and cheese
1 10 3/4oz can cream of mushroom soup, undiluted
1 4oz jar diced pimento, drained
1/4 c chopped green pepper
1/4 c chopped onion
1/2 c milk
1/3 c mayonnaise
1/2 c (2oz) shredded sharp American cheese

Cook macaroni according to package directions, omitting salt; drain well. Add the pouch of cheese sauce from package, soup, and next five ingredients; mix well. Spoon into a lightly greased 2-quart casserole. Bake, uncovered, at 400° for 20 minutes. Sprinkle with cheese, and bake 5 more minutes.