Tire pressure is fine all around. A little puzzling when you put a level on the feederhouse and it is fine, the adapter frame is level with the top of the header as per the book, but drop to the ground and it is left side low!!
About all you can do if everything is on "square" and it still isn't level is add or remove shims on either side of the top of the feeder house. A little debris on top of the feederhouse can change things too.