Here is some info which might help, logically you won't have to do the re lock part, but this should work, even though the steps are for a desire HD
C&P
First of all, this is not my work. This is just a compilation of all the information obtained from various threads and the members of XDA. I claim no credit but just wanted to write this for all who wishes to get back to stock ROM (like myself) either for Backup purposes or Warranty cases. Using the HTC method to unlock the bootloader has given me hell such as Wifi error and stuffs. So here it is
Special thanks to Monx
1. Create a Goldcard (use a spare Micro SD in the phone after formatting with FAT 32) and follow the instructions below
http://www.addictivetips.com/mobile/...htc-desire-hd/
* Instructions may be for Desire HD but it can be used too for our EVO
* Only Procedure 3 is different as all u need to do is use the Goldcard helper
App to copy the Reverse CID to clipboard
2. RELOCK your Bootloader (STEP 14) if its unlocked using HTC method below
http://www.htcdev.com/bootloader/unl...uctions/page-4
3. Download your original RUU ROM from here
http://forum.xda-developers.com/show....php?t=1208485
4. Extract the ROM.ZIP file from the RUU ROM that you downloaded
One method of doing this is here
http://lukasz.szmit.eu/2010/04/extra...c-android.html
5. Once you have copied out the ROM.zip file, rename it to PG86IMG.zip
6. Copy this PG86IMG.ZIP file into the Root directory on your GOLDCARD
7. Power down your phone and with the Goldcard still in
8. Go into Bootloader (Hold POWER + Vol Down)
9. Phone will auto detect the PG86IMG.ZIP, extract and then ask permission to flash. Select "YES" ....or course
10. Once its done...you got your STOCK ROM back. However your bootloader will still show "RELOCKED"