The FAM Section 1, Sheet 3.09 specifies 1.83 to 1.89 between the top of frame and the bottom of the floor panel at the front cab mount, but Section 1, Sheet 3.12 calls for 0.76 to 0.82 between the top of frame and bottom of floor panel at the rear shackles. Maybe the cab floor isn't parallel to the frame. The frame normally would set nose down just a touch with an empty truck. I think the reference dimensions on Section 1, Sheet 1.07 showing them parallel is likely for reference only.