There's a leaked Gingerbread Radio that will work with stock rooted but I don't recommend that unless you know how to disable the Verizon OTA push... otherwise you will end up like a lot of the other members right now with a phone that doesn't work and a screen with an exclamation point.
In order to use that radio.. you need a custom ROM. Example.. Bamf, Gingeritis, CM7,etc... Here's the info on flashing custom ROMs:
http://forums.androidcentral.com/th...estore-install-roms-thunderbolt-new-post.html
There's a link to the Official Thunderbolt ROMs and Kernel listing in the guide... or here is the link..
The Official Thunderbolt ROMs & Kernels Listing v2.5 (Updated 8/26) - xda-developers
You have two choices:
1) Upgrade to the leaked Gingerbread Radio for stock rooted and disable the Verizon OTA push
Or
2) Flash a custom ROM that is compatible with that MR2 radio.
Decide on one and I or someone else will help you in the right direction. The first choice you will have the latest leaked Gingerbread update and will still use the stock ROM that comes with the phone. The second choice is using a custom ROM that will enhance looks, performance, features... etc...
Which path would you like to choose?