SM-N915A lags, freezes and reboots

[oditius]

I had encrypted my phone, but later decided I didn't want it. But now that I removed it, it freezes, lags and reboots randomly. My phone can't be unrooted, so I need to flash the same AT&T rom again. Is that possible? Please don't tell me to do a search, I've done that. Please if you have a way to fix the problem, post a link or step by step. I would appreciate it. Otherwise I will will toss it under a truck and replace it with the warranty.

P.S. I already did a factory reset.