[Transformer TF300T Q&A, Help & Troubleshooting] 1337 H4X0R:
So you want to downgrade to .15.3 from .27.5 with a locked bootloader. Okay, thats easy because thats what I did to get root after I lost it to a OTA update.

DO THIS AT YOUR OWN RISK-I TAKE NO RESPONSIBILITY IF YOU ACCIDENTLY BRICK YOUR DEVICE!!!!

Downgrade to .15.2 from .27.5 or similar.

1. Download the .15.3 firmware for your device and region from ASUS' website. MAKE SURE THE SKU IS THE SAME AS YOUR DEVICE. e.g., I have WW, so I used the WW firmware. To find out your SKU, go to about tablet and in the build no., it will tell you your SKU, eg build-stuff-here.WW.10.more-number.27.1.

2. Extract the .zip file you downloaded twice. There is a .zip inside a .zip. You should end up with a blob file and a folder. The blob file is the one we need.

3. Make sure your device is backed up via the ASUS app backup, and that all important stuff is backed up.

4. Make sure you have the correct ADB and fastboot drivers. VERY IMPORTANT.

5. If you don't have the Android SDK or access to the fastboot/adb command line, download and install this. It's what I use.

6. Restart your PC to make sure your drivers and software are installed properly.

7. Get your device into bootloader mode. You can do this by...

7ai. Whilst the device is connected to the pc, type "adb devices" (Without quotes) in adb to see if your device is connected properly. If you see your devices serial no., it's working properly. Or else, make sure you have the right files and the device is connected to your pc.

7aii. Type "adb reboot bootloader" (Without quotes) and hit enter. Your device will boot into the bootloader.

****or****

7b. Press and hold the volume down and power buttons until it goes into bootloader mode.

8. Copy and paste the blob file to the root of where your fastboot is running from. If you used minimalistic adb and fastboot. Right click the shortcut, click properties and then open file location. Copy and paste the blob file to there.

9. Make sure your tablet is the only android device plugged in.

10. Execute "fastboot devices" (Without quotes) to make sure that your device is set up properly. If you see your devices serial no., it's working properly. Or else, make sure you have the right drivers/software and the device is connected to your pc.

11. If all is well, execute this command.

fastboot -i 0x0B05 flash staging blob

DO NOT INTERRUPT YOUR DEVICE DURING THIS OR YOU WILL HAVE END UP WITH A BRICKED DEVICE!!!!

12. It will send the file to your device. When you see blue progress bar, it is now flashing the blob file.

13. Go make yourself a cup of coffee. This may take a while, and staring at it will only make you anxious. Take this advice seriously.

14. When you get back, it should of successively completed.

15. Run "fastboot reboot" (without quotes" to reboot device.

You should now be downgraded. :D:D

You may/may not have a problem with the launcher (this happened to me). But if you do, follow these steps...

1. You should be able to log in, but then as soon as you do so, launcher force closes.

You have two options.

2. Swipe down on the right side of the status bar to reveal the quick settings, and then click on settings to go to the settings app.

3. In settings the settings app, Select apps, then all apps.

4. Navigate to "launcher" then clear cache then data, then finally force close.

5. Hit hit the home button, and everything should work as normal

****or****

6. In setting, choose launcher and switch to the ICS launcher.

7. Reboot as prompted

This post will be updated with more information soon. I'm proofreading for any mistakes now...

If you want root, use mottochoper, and then install and use the XPOSED framework because it makes your stock rom feel like a custom one. Its pretty straightforward from there.

If you have any questions, just ask, and remember...

Hit the "THANKS" button, it's a good habit to get into.

FYI, I won't respond to your queries in the next 12 hours since I need to have my sleep, you know. It's nearing the darkness of the night in my side of the sorld. Thanks for your understanding. Speaking of thanks, hit the "THANKS" button if I helped you. I spent a lot of time typing this up!