Not all doors are created equal.

When selecting a door, stop off at the tool department first and pick up the longest metal straight edge they have.

Then check each door with the straight edge in length, width and corner to corner. When you find one that's close, check it again at several places in length and width. Do the diagionals in several places too.

If you don't find a door that's flat, go to another building center and check their doors.

Dave