Seems normal. Your GPU just isn't an overclocker :/. I have an FTW with an ASIC of 68.4% and it will do 1455mhz with a bios edited for increased power target, but it isn't a noticeable difference from the 1392.2 stock boost clock so I just leave it at that, but it does still need a higher than stock power target to stay at 1392.2. You'll probably have to increase voltage and power target for even a slight OC.

I was able to get a max clock of 1542 @ 110% power and +25mv with memory at 8007mhz (+500) and temps at 68c full load on the new 970ssc with new power and cooler.  Only problem was that Sims 4 would crash on it, every other game was fine.  So I kept fiddling until I arrived at a stable 1476mhz core OC and the same 8007mhz memory and +25mv.  25mv was the most I could put on the card before it stopped boosting.  my ASIC is 62.3% so I really never pay much attention to that number bc it's usually not the best indicator.  Coupled with a 3570k @4.0ghz I'm still better than 93% of results on Firestrike and coming from a 670, I am in love with this card.  Don't care about the memory "scandal" everyone is going on about bc I only game at 1080p 144z Asus monitor.  Perfect for me.  Your card is still amazing, it just doesn't overlock well, but I would do like the others said and give some voltage to it, also set up an aggressive fan curve or you will def be 70c+.  My current temps with the down clock is about 66c max load.  Good Luck and enjoy your card!

mongoo_de
Default 1380mhz @ 1,193 V @ 75 Grad  Celsius -  asic 66
20 mhz more ok 
Another 20 Green pixels in Firestrike
Mem over plus 300 Pixel error
 
Is this normal ?
Maybe rma?
 
Greetings

Your video card is guaranteed to run at the default clocks. Overclocking is not under guarantee. In addition overclocking has a lot to do with the integrity of your system and setup.