Amberjack and Lesser amberjack are the ones that are hard to figure out. An almaco jack is flatter but top to bottom is a bigger. and the have a much darker appearance.
Hope this picture will show up. There several almacos here. The 3 on the right are almacos. only 3 amberjacks that day.
From left; amberjack, 2 almaco, amberjack, cobia, amberjack, 3 almaco.