Hi, have had an issue with my sm-t550 for a while where it randomly restarts (normally on WiFi and when just getting to a good bit on Netflix) it may happen once in 7 hours or 10 times no way of knowing

So I wanted to install custom firmware, I followed an xda guide and rooted it installed a recovery, was directed here for firmware but all I see is deflated stock (which is booting now) if I go to asop I can't see any posts, same with stock. How long do you have to be a member to see them? Ideally I want to install android 6 (I can't do it ota as when I choose update it says I have modified it in an unauthorised way....which..well... I have)