FIX for 1X DATA
-Go to the ThunderBolt's phone dialer. Enter ##778# and hit Send.
-You'll get a pop-up labeled EPST, with the choice to "View Mode" or "Edit Mode." --You want "Edit Mode."
-You'll be asked for a password. It's 000000.
-Now flip down to "Modem Settings," and then choose "Rev. A."
-Change the setting from eHRPD to "Enable," hit OK, then press the Menu button on the phone and tap "Commit Modifications."
This gave me 3G back, hopefully works for others.