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.
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.