Looks like I got my T399 after you all got most of the bugs worked out. Saw in another post folks were waiting for Kitkat 4.2.2. That is what I upgraded to the second day I had the phone. Anything I should watch out for?
I would start by making sure you have the latest software. I upgraded mine the day I bought it. Settings, More, scroll down and select About Device. Finally you get to the software update option.