Shunshin is when you focus chskra into your feet to increase your speed. Sasuke, Sakura, Naruto, Kakashi, and a ton of others used this before in part 1. Your speed and distance is decided the amount of chakra you use, A's chakra was said to be increasing to Bijuu level as Karin put it and he said he was using Shunshin. Naruto in KM and up uses Shunshin.
FTG have been called Shunshin by Rin, Tobirama, and I think Shikamaru or soneone in the alliance. It is possible that Naruto have FTG or that he mastered Shunshin to high levels. Naruto's own chakra reserves was already high during the war time, this is like 10 years later so his reserves should be really high.