Lg D802 hard reset after phone system become slow!!

Hello everyone,

I have a lg d802 phone that was problem google account. i made it hard reset after phone become very slowly! then i try to reflash phone but nothing change. many way i made it downgrade upgrade but problem is still there.

I use Lg tool flash 2014, ouctopus box, setool box but evryone give me same result. is there anyone know that problem? if know please guide me. i am stuck on this problem.

Thanks in advance