[Salone]

Well, military vehicles aren't too focused on fuel efficiency. Given that the apocalypse happened, I'm not sure how many resources were shoved in to developing fuel efficient/alternate energy vehicles. But an APC is the lovechild of a tank and a humvee, and able to carry anything that both can. And generally, they come mounted with guns big enough to repel everything but actual tanks. Besides, a diesel engine? You could put anything in there, so long as its combustible.