So in light of this there is a simple way to do this without installing the froyo PG06IMG.zip and going through the hassle of downloading all the firmware OTA's to get back to stock 2.3.4 firmware. I have used this method and it works great. You must be rooted with s-off for this to work. If your running a custom rom that is not sense based or based of the stock HTC sense roms, attempting to run a RUU will fail which makes this method usefull for anyone on any rom
More information can be referenced from HERE
Note: if you rooted using the method from HERE then you should already have all the requirements for this to work.
2) Android SDK
Once you download the sdk place it in the root of your C: drive and rename it to something easy like "android" or "sdk". Go into your sdk\tools folder and double click on the android file or right click on the file and select open. It should open a command prompt and then load the sdk.
INSTALL PLATFORM-TOOLS ONLY!
3) Download and install HTC Sync necessary for drivers in using adb and fastboot
4) Install a md5 utility like WinMD5Free for checking the hashsums of the files.
Unrooting back to stock 2.3.4 firmware
WARNING: This will completely unroot your device. I or xda will not be held responsible for anything that may occur to your device if you do not follow the instructions properly. You have been warned!
5) Download the 2.3.4 hboot
Check the MD5sums of the file hboot_0.99.0000.img: 3008853f805b107fda434ce623f43318
If the MD5sums do not match the above numbers DO NOT CONTINUE
Place the file in your platform-tools folder in the android sdk
6) Download the 2.3.4 ruu
Note: MUST DOWNLOAD THIS FILE ON WIFI ONLY BECAUSE OF THE SIZE
Check the MD5sums of the file RUU_Speedy_S_Sprint_WWE_2.77.651.3_Radio_1.08.01.0 111_NV_SPCS_2.97_01206_PRL60674_release_237263_sig ned.exe:
Again if the MD5sums don't match the above numbers DO NOT CONTINUE
7)Plug your phone into your usb cable to your PC and make sure "USB debugging" is enabled on your device under Menu >> Settings >> Applications >> Development
open a cmd prompt (start button then type cmd and enter) and cd to your sdk\platform-tools folder.
Example: cd C:\android\platform-tools or cd C:\sdk\platform-tools
8) adb reboot bootloader
Make sure the device is in fastboot mode (a lot of times it's not). It should say fastboot in red letters on the top.
9) fastboot flash hboot hboot_0.99.0000.img
If all goes well you should see "s-on locked"
11) Make sure your phone is in fastboot mode once again. Next run the ruu file and follow the instructions to install the factory images of 2.3.4
Congrats your phone is now back to stock 2.3.4