Using AT&T HTC One on iWireless topic

I bought an HTC One AT&T that I unlocked then rooted and installed CM11 using the new CyanogenMod Installer. The issue is that I live in an area where you can only get decent cellular speeds using CDMA (Verizon, US Cellular). There are two GSM carriers however, one that is so old, it doesn't offer anything above EDGE and iWireless, a T-Mobile affiliate. I wanted to use it on iWireless, but all they were able to get was EDGE speeds when they tried it on my One. Is there someway to make it accept at least 3G speeds? Maybe by flashing the radio or something. I've never really done more than rooting and installing a ROM, but I'd be willing to try it if it was possible. Any help is greatly appreciated.