Eddie Jones says England need to add more consistency to their game if they are to become the world's best Test-playing nation.
England completed a historic whitewash of Australia in June, securing a 3-0 series win with a victory in Sydney in the final Test.
The national side are second in the global rankings and have won nine straight matches under Jones following their poor World Cup campaign, in which they were eliminated at the pool stage.
But despite making huge improvements, Jones feels England will not be able to consider themselves the best team in world rugby until they improve their consistency.
"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 HQ. "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."
But while Jones accepts there is some work to do for England to overhaul world champions New Zealand, he was satisfied enough by his side's mental toughness under pressure to draw a comparison between them and the all-conquering All Blacks.
"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," he said.
"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."