I found reference to the origin of the term Josh on page 89 of the "Annals of the Army of Tennesee and Early Western History" :
"The troops of each State, received in the course of the war, nicknames, by which they were familiarly distinguished. The Texans were called 'Chubs', the Arkansians, 'Joshes'. The latter sobriquet ordinated in this way: There was a man in the Third Arkansas Calvary named Josh, who was conspicuous for his height and size, and from this circumstance his name soon became familiar throughout Forrest's Calvary. In time the Third Arkansas were dubbed 'Joshes', and then the term was applied generally to all Arkansians.