Orcon, Slingshot and Snap all improved their web-browsing speeds in July while Vodafone and Telecom slowed down, according to broadband testing service TrueNet.
Despite its slipping performance Vodafone regained the lead in the copper-line market from Telecom, downloading a test web-page in under half a second.
Telecom fell to third place in the tests during July, and is now behind TelstraClear's copper-line service.
Orcon and Snap improved in the latest rounds of TrueNet results, downloading the test page in an average of just under 1.5 seconds.
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Slingshot also improved during July and took a little over a second on average to download the page.
TrueNet's John Butt said these three internet providers all showed "significant" - and unexplained - gains in performance after July 11.
But Butt called on internet companies to do more. "Most [testing] probes still can't match the expected time of 0.4 seconds.
"ISPs have more to do to improve the performance of a very large numbers of customers," he said in commentary to the results.
While Vodafone led the copper-line market, TelstraClear's coaxial cable network - available only in Wellington, Kapiti and Christchurch - still offers the fastest service.
TrueNet's measurements are drawn from over 300 test sites around New Zealand, which probe the speed and performance of nine internet companies every hour.