I am starting to think this is something with the recent Motorola radio software...
I have a Thunderbolt and a Razr M. Before the Razr M, I had a Razr MAXX.
I use them side by side, one for work and one personal.
I used to get solid 4G/LTE *all the time* and rarely ever 3G on either phone but after the most recent Razr MAXX update I noticed my Razr MAXX would often struggle to stay on 4G/LTE while my Thunderbolt was solid 4G/LTE.
I bought a Razr M the day it came out to replace my Razr MAXX and it's 4G/LTE performance has been *identical* to my (post-most-recent-update) Razr MAXX, struggling to stay on 4G/LTE half the time.
I had to exchange my first Razr M for a new one because the power button stopped working after a couple of days, and my replacement Razr M has the same 4G/LTE issues.
Meanwhile, side my side, my Thunderbolt rocks 4G/LTE *solid* 24/7/365.
I might try to see if I can flash back to GB on my MAXX and see what the 4G/LTE signal is like...