If you have OTA'd past 4.3 its just a simple download the images from toms server for 4.3 and fastboot flash them.
You can get the stock 4.3 images from : http://rootjunkysdl.com/?device=Tegr...%20Stock%204.3
These files here is infact CWM/TWRP flashable zips so its just a case of unlocking the bootloader and flashing either CWM or TWRP then placing the stock 4.3 rom zip onto a SDCard and flashing it.
But before you flash the zip make totally sure you wipe the following partitions
This will downgrade you back to 4.3