i had exactly the same problem with you for five days before a week and i made exactly the same actions,thaughts as you do but everything went back to normal one day so i supposed that was the network (t mobile) and not the phone so my advice to you is relax and leave some days to passing and am sure that all gonna be right and back to normal soon.T mob make upgrades to the network so it's expected i think....
sorry for my poor english but am 4 months only in the states.