In the problem areas, please do the following and report back with what band your phone is connected to. To find this information, follow these steps:
1: Open up your Phone application
2: Dial the following number exactly as it appears. Hit the call button when done: *3001#12345#*
3: Click on "Serving Cell Info
4: Look for "Freq Band Indicator." Note down and report back with this number. You will see either "13" "4" or "2"
5: Look for "Downlink Bandwidth" and "Uplink Bandwidth." These values may be empty at first, but should populate within a minute or two (keep the screen awake). Note down the Mhz value (will be 5Mhz, 10Mhz, 15Mhz, or 20Mhz).