So I recently repaired a Galaxy s4 device. I put new front glass on the phone. When I activated the device I noticed that the phone would not connect to the 4g network, instead it would fluctuate between 3g and 1x. My searches led me here and so far these are the steps I have taken.
Switched Mobile Data On/Off several times.
Power cycled the device.
Removed SIM card and reboot after a few minutes.
Factory reset the device.
Took the device to my local Verizon store, they replaced the SIM with a brand new one. 4g LTE worked for all of twenty minutes and has since dropped to 3g/1x again.