Help Galaxy Grand I9082 - very slow when internet enabled.

Whenever i enable my "Mobile data" or "WIFI" my mobile (Samsung Galaxy Grand I9082 ) becomes too slow, every task from then on takes atleast 10 to 15 secs to complete, like opening the browser.. enabling the keyboard.. typing the text.. attending to calls.. everything is too slow..

Things i tried :
1 . Rebooted the mobile and tried - issue extists.
2 . Uninstalled all the apps i installed one by one and checked - issue extists.
3 . Done a complete factory reset. - issue extists. :-(

I appreciate if anybody can help me on this issue.