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I have not tried Rootkit v8, but I have used EasyFlasher. Use this guide to get the drivers for easyflasher ready to go with your tablet in APX mode: http://www.transformerforums.com/for...rom-tf101.html
Instead of flashing recovery, download the Asus 188.8.131.52 firmware, unzip it once and place it in the EasyFlasher asusupdate folder of EasyFlasher.
Then flash the US firmware.