At first I thought the ceiling was poorly taped until I laid a long straight edge against it. Now I know the ceiling is actually sagging between the trusses. After a little research it looks like the builder used 3/8" on the ceiling. If I were to layer 5/8" going 90 degrees to the original drywall would that fix my problem? Or should I just ignore it because I really don't want to pull the ceilings down. Thanks!