Check with other people using TMobile in the same spot you're getting bad reception. That may just be a dead spot for them. (Sprint covers this whole town pretty well - but there's one house that gets solid Verizon and AT&T signal, that gets absolutely no Sprint signal at all. Not bad, not terrible - nothing.)
You might just be using the wrong carrier for where you need signal. (The first thing in choosing a carrier is to check the spots you need signal, using that carrier. If you don't get good signal there, change carrier. [Most people go by either price or which phones the carrier sells. A great phone on a cheap carrier is useless if you don't get signal.])