The Kyuubi gave Naruto chakra to summon Gamabunta.Naruto mentioned how he ran out of chakra when he made all those clones.
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Yet a few seconds later he summons Gamabunta.Futhermore,Jiraiya even said Naruto did not have enough chakra to summon Gamabunta,and would need to use the Kyuubi's.
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And later Naruto himself ask for chakra.
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At the time Sasuke did not know the Kyuubi was inside Naruto powering him up.
From seeing how weak he was compared to Itachi,Sasuke left Konoha in order to gain power so he could kill him.It wasn't simply from seeing Naruto fight Gaara.
Everytime the Rasengan,and Chidori ever clashed they equaled.Rasengan doing more damage to a building doesn't put Naruto above Sasuke.