Hello fellow Gainesville T-Mobile customer! The home I moved into about 2 years ago had poor reception, but I was able to get a free repeater from T-Mobile. Just call 611 and ask about it.
This will help if you're able to get a consistent signal at least one bar somewhere in the residence. Of course your luck may be different getting a free repeater since it's at your girlfriend's apartment.
The building I work in has very thick walls so I'm in the same boat as you there, but I just rely on Google Voice over WiFi to get me through that.