He can either lower his Calorie intake or increase his work output. Given his stamina issues I would wager that he needs to switch from doing less resistance training and more high intensity endurance training. Just a thought
I wouldn't lower his calorie intake I'd simply do what you say there decrease the resistance **** and get that big man moving a lot more. He will lose some muscle and "soften up" a little bit. He don't need to be skinny to improve his stamins
ive got no problems with Joshua’s treadmill drill. I’d just apply it off the treadmill, and with greater purpose. Have him working the pads in a ring, but have the guy on the pads applying intense pressure for 3 minutes. Hell, let’s say 4 minutes. Give Joshua a 40 second break, not a minute. I’d want Joshua spitting fire, so when it comes to fight night, dealing with a pressure fighter is a breeze, in terms of endurance. I would ask him to do more than flick out a lazy jab as well. Make uncomfortable become comfortable, before it becomes the norm, before you then thrive from those circumstances.