I am sorry you are having issues with coverage with the new phone. You did the right thing by keep GPRS on. How many bars do you get and are you showing 3G/4G signal? What signal did you have on your old devoce?
You check this Document http://support.t-mobile.com/docs/DOC-2554 for further help with signal.
If you are still having issues please contact our support chat http://support.t-mobile.com/community/chat
Thanks so much for posting
On the phone I'm having issues with(Sparq), I'm currently getting 2 bars with the G symbol next to it. On the samsung SGH T139 I'm currently getting 3 bars of what I assume is just standard cell phone signal. As far as the samsung Behold goes, I know I would recieve 3g signal on it with about 3 bars aswell. I noticed that if I go to a location about 3 blocks closer to the city I can turn off my phone and turn it on with no problem getting signal. Once I move here I still have decent service. But, if I turn off my phone here in my apartments, and turn it back on, It's pretty much impossible to recieve service. So I essentially have to go to an area where I can get service, then come back here.