Green’s Dictionary of Slang

(US) an arduous journey; hard walking.

1982		(con. 1970) J.M. Del Vecchio 13th Valley (1983) 248: The men of 3rd Plt were sweat-drenched and breathing hard from the hump.
2003		(con. 1989) A. Swofford Jarhead 53: I was a hard bastard, that on humps my platoon handed the heaviest gear to me and I carried it without complaint.