Board Thread:Episode Discussions/@comment-25319479-20180517110054/@comment-32685487-20180520190342

Even two times a 3 tier in chakra makes it a 6 tier. Kurama's chakra since birth has been leaking into Naruto, transforming into his own chakra. So Naruto has ALWAYS had massive chakra.. he only lacked the chakra control to manage it properly for most of P1.. so him making 1000 shadow clones by himself is completely understandable.