[HTC Sensation] Skipjacks:
You're over engineering this. You don't need to root your current ROM first. That's an extra step since you're s-off.

If you are s-off it's really simple to get 4EXT recovery.

First, download this and put it on the root directory of your SD Card (meaning not in a folder, just on the SD Card. Do not rename it)

http://d-h.st/qnm

I got this download link from here...

http://xdaforums.com/showthread.php?p=21989107

Click Thanks for Joaquinf in that thread. He made the 4EXT zip that's flashable through the bootloader.

That is 4EXT made into a zip file that's flashable via the bootloader, which you can do when you are S-off.

So put that file on the SD card, power the phone off, pull the battery out for a second and put it back in (this stops fastboot so you can get back to the bootloader). Then hold volume down and power at the same time. You have to hit both buttons at the same time. If it goes to the splash screen, pull the battery and try again.

When the bootloader loads up it will immediately find the PM58IMG.zip file. It will ask you if you want to install the update. Say yes by hitting volume up I think (it will tell you how to say yes)

Put the phone down and don't touch it until it tells you it's done. Should just take a second. But seriously don't touch it. Leave it alone.

If that works, you've just flashed 4EXT. You can check it by pulling the SD card out (so it doesn't try to flash the PM58IMG again) and rebooting to the bootloader and selecting 'recovery' from the menu. 4EXT should boot up.

This entire process so far shouldn't take more than 3 minutes total. It just sounds like a lot.

To see this detailed out by someone else in case you want to check what I'm saying, read steps 4 and 5 of the first post in this thread.

http://xdaforums.com/showpost.php?p=21989063&postcount=1

Give the author 'thanks' again because he's awesome and deserves it.

Now you've got 4EXT installed. Great. You're 1/3rd of the way home.

Now you need to update your firmware. Delete the PM58IMG.zip file you used to flash 4EXT off the SD card (use a card reader or boot the phone up and delete it, whatever works. You can also use 4EXT as a card reader now too by choosing USB storage from inside 4EXT. It will give you access toteh SD card on your computer now)

Now get new Firmware from this thread.

http://xdaforums.com/showthread.php?p=21711154#post21711154

try the 3.33 firmware universal. First download link in post 2 of the thread above.

CHECK THE MD5 SUM!!!! I'M NOT PLAYING AROUND HERE!!! You are worried about bricking your phone, this is where you can do it if the firmware .zip is bad.

Put that PM58IMG file on your SD and flash it in the bootloader the same way you flashed 4EXT recovery a minute ago. (If you're still in 4EXT recovery you can use it's power menu to reboot into bootloader easily.)

This will take a minute. The phone will shut off and go black in the middle of this process. Your heart will skip a beat. Relax. It'll come back on. Again, put the phone down and walk away while it does it's thing and don't touch it until it says it's done.

Delete the PM58IMG file from your SD card.

You are now 2/3 of the way there. Your phone WILL NOT boot up right now because your ROM is not compatible with your firmware. Relax. That's supposed to happen.

Now you can flash CM10. Make sure you have the CM10.zip file on your SD card nad GApps. (Bruce has Gapps in his downloads page). Delete the PM58IMG firmware file from your SD card (that's important)

Pull the battery again so you can get back into bootloader. Get into bootloader (power + volume down)

Select Recovery

4EXT should boot up.

Go to the Wipe menu. Wipe all partitions except SD card. (Old ROM is now gone)

Go back to the main menu.

Install from SD

Find the CM10.zip file you should have downloaded and put onto the SD card. Flash it.

This will take about 3 minutes. 4EXT will flash it and ask if you want to reboot. You do not yet. Not you need to flash Gapps the same way you flashed the ROM.

When that's done, now you can reboot. You shoudl see the CyanogenMod boot animation after the splash screen. Give it a few minutes to boot up this first time. Once it boots, set it up the way you like it. If you enjoy it, donate a few bucks to the developer, Bruce.

You don't have to root CM10. It's already rooted when you boot it up the first time.