I'm wondering if my Galaxy S3 is starting to suffer from Sudden Death Syndrome?

For 5-6 months my S3 has been becoming more and more sluggish at various times with some actions taking 10-15 seconds to complete.  For example - hitting the dial button on a contact it will sometimes freeze for 15 seconds before it starts dialing. 

Over that time I've also been getting an increasing number of random freezes and reboots.  

Over the last few days the phone has started locking up fully - the screen is still on but all input is unresponsive.   I can still be reboot it by holding down the power button for 5+ seconds but nothing else. 

It's now at the stage where I'm seeing freezes and reboots 5-6 times a day. 

I've run the eMMC check and my phone does have the "Insane" chip. 

The freezing / sluggishness issues started happening well before the last firmware update but are continuing to get worse so I'm thinking damage may have been done before the firmware update that was supposed to fix it. 

My S3 has only ever run stock firmware from 2 Degrees. 

Is this the final stages of SDS before the phone dies? 

Or is SDS recognised only when the phone finally dies? 

I bought the phone from 2Degrees last year. 

Suggestions & strategies? 

I have yet to do a full factory reset to see if that makes a difference and can get that done.  Or should I get into 2Degrees fast before it packs up fully? 

Thanks!