Red Devil rx 480 8gb help

Hi,

mobo: Asrock h81 pro btc r2
GPU: PowerColor Red Devil rx 480 8gb
Cpu: Intel celeron 1840
8gb Ram and 1250W psu
OS: Windows 10

For a week I have been trying to stabilize my rig with 6 Red devil rx 480 8gb. I am using boysie's rom https://forum.ethereum.org/discussion/10382/boysies-31mh-rom-for-rx480-red-devil-v2.

With 3 gpu's connected to the motherboard everything runs ok.

After connecting a 4th gpu, after 10 seconds of mining the hashrate on one gpu drops to 0 and I get the error "Gpu hangs in OpenCL exit". This happens also with 5 and 6 gpus.The only advice I have received/found is to lower memory clock and adjust power.

I have tried everything between GPU: 1100-1180MHz, Memory: 1950-2250Mhz, 930-1000mV.

Nothing seems to work. I have tried new drivers, old drivers (currently 16.9.2). I have tried different timings and different bios. Where is the problem? I am sending these cards back on monday if I cant get them to run.

Ps: The rig worked fine with previous cards( Sapphire nitro rx 480 8gb, micron)

Thanks in advance