Naruto Uzumaki never became a chunin. A chunin is the second lowest rank in the Shinobi world( above Genin).
To be a chunin, one has to pass a certain exam, which can be written or physical, or both. During Naruto’s chunin exam, village hidden in the leaves was attacked by Orochimaru, and the chaos spread all over the village. During that time third Hokage, Hiruzen Sarutobi dies while fighting with Orochimaru. So they were unable to continue the chunin exam and Naruto was not able to pass it.
It is quite surprising that the most powerful shinobi of his era has never become a Chunin as technically he has not passed the chunin exam due to the attack by Orochimaru.
Naruto Uzumaki became Hokage and controlled the power of Kurama which was quite impossible but never became a Chunin.
