HTC Thunderbolt revolutionary, ota update accidentally installed

[Frandiglious]

NEED HELP! i have an HTC Thunderbolt. i rooted the device with revolutionary. shortly after, i accidentally accepted an ota update to the latest firmware. now, when i try to get into recovery, i get a white HTC screen, and then the update screen (black with a picture of the device and a green downward arrow) and after a few seconds, the arrow turns red. the device is fully functional, but i can not get into recovery. i would like to clear the cache and re-root using a custom rom to avoid this issue in the first place. i am new to this so any help would be greatly appreciated. i have found a couple of videos on youtube on unrooting, but the stock firmware file needed to do so has been removed from the internet it seems. any ideas??