Facebook app has been known to cause these problems on the razr. Not only is it a battery hog, it also causes other problems. Other apps could be the culprit too. Also, not every tower has 4G, and you may be actually connecting to a tower further away from the 3G tower, and thus you will see it switch back and forth between the closer 3G tower and the further away 4G tower. I notice that at my house. When I lose my 2 bars of 4G, 3G comes in at 4 bars, so I know my phone is trying to connect to a tower further away for 4G. i did remove my Facebook app and then did the following. it will make your phone more stable.
Turn phone off.
While off, press and hold both volume keys and power on phone.
Press volume key down to highlight recovery and then press volume key up to boot into recovery. Then you will see android icon with triangle.
Press both volume keys.
Choose clear cache partition using down volume and press power button to clear cache.
Highlight reboot / restart and press power and your phone will reboot.