Ok this works. confirmed on mine.
My evo was on unrevoked 3.21. Wanted to update to 3.29.651.5:
download this:
Multiupload.com - upload your files to multiple file hosting sites!
quote from xda:
"Place OTA_Supersonic_3.29.651.5 on your SD cards root folder. Power off and reboot holding Volume down. Once the bootloader is up goto recovery so clockwork loads up. Choose apply zip from sd card. Choose select zip on sd card. You will see the OTA file on the list flash it. Just wait for it to install it will reboot the phone show a progress bar reboot again they show a percentage etc it takes a few minutes.
Now you have the update installed, but the update removed clockwork and root."
apply unrevoked 3.21 again!
there you go, root + 50plus fps