mobile

Hi, I've been searching for a solution for failed Lollipop update on my AT&T device. I bought my device with AT&T and switched to T-mobile with sim unlock a year later. I'm currently running N900A...NC2 (4.4.2). My device is rooted but i haven't done much after rooting it except removing some bloatware. I'm able to download the OTA update that AT&T is pushing (at least i think its the lollipop update). However, after download the installation fails. I don't know if this is because i'm not with AT&T any longer or is it because my device is rooted. Tried calling T-mobile with no avail. Wondering what my options are at this point.

I read in a thread here that DO NOT FLASH other carrier's stock firmware with ODIN. How true is that? I'm pretty novice at Android devices. So any help/suggestion is appreciated. Thanks in advance.