Ford's F600 is fitted with a steering axle rated at 7,500 pounds. I would be quite surprised to see an axle (not axel), fitted to an FG that had an 8,000 pound GAWR unless it came from the aftermarket (Fusion, Crane, Dynatrac, Meritor, etc.)
GVWR is 22,000 pounds and GCVWR is 43,500 pounds on...