Just another thought. Could the door opening be out of square? If you have , or can borrow, a carpenters framing square you can check the opening for square. If you can't get a carpenters square you can check it with a tape measure by measuring the diagonals. Upper left corner to bottom right and then upper right corner to bottom left. If the opening is square the measurements should be the same. You could do the same for the door itself.
2000 Monaco Diplomat 40PBD
2012 Grand Cherokee Limited
2008 FatBoy, three spoiled Great Danes and a cat.