Why can't i get 4g speeds when using wireless tether app to my laptop

[spediegunz]

I turned on my 4g on my phone and ran a speed test with the speedtest.net app it confirmed that i was getting between 7-9 Mb down which is pretty fast and considered 4g speeds to me then i fired up the wireless tether app on my rooted unrevoked htc evo phone with regular firmware and the latest radios and what nots and connected my laptop to this wifi connection established by my cell phone ran a speed test on my laptop through speedtest.net and multiple other speed measuring sites and they all said i was getting about 400-600 kbps so my question is why can't i tether in at the 4g speeds that the speed test are confirming that im getting I've done some searches and found a few concerning the same or similar issues but nothing i read through seems to offer a working solution can anyone explain to me why is this happening and if it is possible to fix and how?