Apparently, there have been a flood of 4G disconnect issues for many users of the new HTC Thunderbolt. The issue is wide-spread as well, from Florida to California and everything in-between. Reports indicate that LTE disconnects randomly, and then reconnects 5-10 seconds later. Luckily, Verizon is aware of the problem and is working on an OTA update to deal with the issue. Sound off in the forums if you are one of the unlucky users that have experienced this issue.
Source: TalkAndroid