even after orochimaru screwed up his seal, Naruto was able to do hundreds of kage bushin, henge, and fight the entire night vs the illusion ninjas, so basically even on his own he has abnormally high stamina.

Also in episode 1, Naruto performs a 1000X kage bushin without the kyubi. In the anime if you count them I think there is like 300 clones on screen but in the manga Iruka says he multiplied more than 1000 times.