[Q] Samsung Galaxy Note 2 SGH-i317 AT&T Question and help

Hello Everyone

I have a Samsung galaxy note 2 from AT&T

I bought it from fry's and it was suppose to be an unlocked phone
any way I rooted the phone and started trying different ROMS

the phone is an AT&T stamped phone and my carrier is T Mobile by a sim card

when you get to the carrier choice on the rom install do you choose AT&T as the carrier or T Mobile???

playing around I have gone both ways to see if it will work

my currant rom I like is the Jedi x20
but when I install Jedi master x2 I can get it installed after two or three try's but then after awhile I lose my data connection and can not get it back!!!!????

I really like the Jedi master x2 but since it is for the t mobile phone I take it it wont work on the at&t phone??

Samsung Galaxy note 2

I am not to savvy on this custom rom stuff
I have read about the knox counter thing and for me I do not care what Samsung thinks
the way I see it is this way like Xbox, PlayStation, and now these cell phones someone somewhere will find a way to
try to make it better faster slicker and to get out from being held by the restrictions ( I was going to say the man But I think you all know what I am trying to say!)
Again my mind might be able to do a lot of thing but figuring out computer code or cell phone code, hacks, tweaks!!! is beyond me!!!
I think a lot of other people are like me!!

question when installing a custom rom with multiple carrier choices do you have to chose the carrier you are currently using or the carrier
the phone came as? like my phone is branded AT&T I have flash my phone both ways one as SGH- i317 AT&T and now as SGH-t889 T Mobile
it seems to be better setup as a t mobile phone

next my android version is 4.1.2
I have flashed this phone with the Jedi Master X2 it seems that this rom is android 4.3 ?? it has wifi calling and everything else my currant rom does not have Jedi x20

I have also read that if you go to android version 4.3 you can not go back to 4.1.2 is this true???
because if you can't then my phone says you can because when Jedi master X2 data stopped working I went back to Jedi X20
my question here is why on Jedi master X2 did my data connection stop working???