One problem I had with the sammobile website is that I couldn't get the ROM to download from either of the mirrors, ended up having to get it from stockroms but I thought the stock ROM was what I currently have? I haven't done any updates to the software as far as I know, and I've had the Note 3 since about a week after it's T-Mobile release.
If you are already rooted with knox 0x0, you must be currently on MJ2 or earlier. Even stock roms are updated officially from Samsung, which is what sammobile provides.
A newer version of the T-Mobile stock Rom should be available. I don't use the stockrom website, so I can't help you there, but if you go to www.sammobile.com/firmwares/2/ You can search for the latest Rom and you can may find a PDA version which is MK2 or even newer. Then use that PDA to search it on stockrom or try your luck with Google.
Downloading firmware is perhaps the most frustrating thing for this rooting method.
Sent from my GT-I9300 using Tapatalk