Default T-Mobile Signal

I have prepaid 30/mo with T-Mobile. My phone had issues with 3G for some reason so I run on Edge all the time. Certain places in my house my signal drops but a foot over its there. I tested with my sisters phone, also a p880, and she has 2bars+ in those areas. She's running stock ics(maybe JB idk) and I'm running Omnirom KitKat. Any reason for my phone sucking? Any fixes?