How is the best way to level the deck on a craftsman 42 inch cut mower. Have replaced the quill assembleys... one side is cutting lower than the other... have followed instructions from manual but still no difference.

Hi,
Usually there is a hanger on the left, some have them on both sides, that is close to vertical with a nut on the bottom. A cross piece rides above the nut that attaches to the deck and the frame. Turning that nut up or down is the side-to-side adjustment.
Of course, tires must be done first, 14psi front and 10psi rear. Use a level surface.
I once saw a person who had a tire plugged at a service station and the attendant overfilled the tire to make sure it did not leak. He did it to the extent that it separated the fabric inside from the rubber exterior making the tire into a "balloon." There was no hope under this circumstance, but a quick "eyebaillig" from the rear showed the machine was not level to begin with (the whole machine.) and that is also why you do the tires first.
Peace,
Clarke