The 2 by 4 and hammer idea must be from our builder, and now the doors will not shut/latch in the door frame trapezoid. Make an evaluation of the cause and how it can be repaired before shaving/shimming/screwing. A laser level revealed the real problem. Several construction folks have suggested we add beams to halve the joist lengths on both sides of the single center beam that now runs the width of the house. A crawl space, plumbing and duct work will make it a real challenge. When done correctly, I believe I can adjust doors and fix cracks just once.