Downgrade 7840 to KitKat?

Seems that with every "update" my 7840 gets slower and slower. The latest 5.1 has made things unbearable so I am looking to go back to KK, root nice to have but non essential. I installed the latest drivers and downloaded IntelAndroid-FBRL-01-17-2015 per the rooting thread, but when I try to run launcher.bat I get the following

Code:

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copy needed files to our device
target reported max download size of 536870912 bytes
sending '/tmp/recovery.zip' (3477 KB)...
OKAY [  0.390s]
writing '/tmp/recovery.zip'...
FAILED (remote: Bootloader must not be locked)
finished. total time: 0.667s
target reported max download size of 536870912 bytes
sending '/tmp/recovery.launcher' (469 KB)...
OKAY [  0.278s]
writing '/tmp/recovery.launcher'...
FAILED (remote: Bootloader must not be locked)
finished. total time: 0.546s
target reported max download size of 536870912 bytes
sending '/sbin/partlink' (158 KB)...
OKAY [  0.281s]
writing '/sbin/partlink'...
FAILED (remote: Bootloader must not be locked)
finished. total time: 0.547s

issue fastboot oem "stop_partitioning"  command to start cwm recovery:
...
FAILED (remote: command not allowed in this device state)
finished. total time: 0.394s

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This thread suggests that what I am trying to do may be impossible
http://forum.xda-developers.com/dell...itkat-t3157770

What are my options here. I am pretty much ready to throw the tablet in the trashcan if I can't remove the atrocious 5.1 update.