Slow card on 6x rig.. Help

[Mihair8]

I m new to mining.. Just set up my 1st rig.. 6x rx580.. With claymore I'm dual mining etc and sia coin.. But gpu04 is about 15/20% slower then the other cards.. How do I figure out witch one is it.. In witch pcie it s in?
The other ones are getting around 29m/hs and it's been running 3 days with no problems.. At 900w..
I put in the parameters for downvolting and oc memory temperature and fan in the claymore miner bat file.. No flash bios..
Any help or good ideas?