If England are to become the best rugby team in the world, coach Eddie Jones said they must develop consistency.
England have quickly climbed up the world rankings since Jones replacing Stuart Lancaster November last year, guiding the nation to an historic series whitewash of the Wallabies in Australia.
June's 3-0 victory came after England claimed the Six Nations grand slam in March, with Jones and Co. now unbeaten in nine consecutive matches to be ranked second in the world.
But Jones insisted there is still room for improvement.
"While we had periods in the Test series, we weren't consistent enough and that's something we need to develop if we're going to be the number one side in the world," he told Sky Sports News. "There's a fair bit of work to go into that.
"Discipline was excellent, and I was pleased with our mind set, our toughness when it came to absorbing pressure.
"One of the interesting stats was that they made more line breaks than we did but our line breaks resulted into more points and so we were able to convert pressure into points - that's what top Test rugby is all about.
"We won the last 20 minutes of all three Tests and that's extraordinary and shows their mental toughness."
Jones added: "Physicality is always a big part of it but it has to come with a mental toughness too, and what is mental toughness? It's being able to perform under pressure and we're developing that.
"It's when the heat is on and the pressure is on - you've got to make those right decisions and that's what New Zealand did in their series against Wales."