An earlier post said to try an app that can change the thunderbolt between 4g and 3g.  I am trying an app called LTE-On/Off HTC Thunderbolt.  I have only used it one day, but I can actually see a difference in my service, especially at home where there is no 4g coverage.  I hope this fixes it permanently, but will post if not.  Why do the customer service reps act like they have no idea that this is a problem?