mobile

I recently switched carriers and took my unlocked SGH-I747 to T-mobile. It's worked decently though not as well as it did on AT&T. I subsequently rooted the phone.

In looking through the settings, in the "Network Operators" list, it does not show T-Mobile. It only shows AT&T, Verizon and 31160. Is this an issue and if so, how can I select T-Mobile as the Network Operator? My apn settings are for T-mobile.

Thanks.