Your psu has 2 x 12v rails with 30A on each. I know my old 780 recommended 42A on the 12v. To achieve this you would need to be using both rails which means 2 cables from the psu to the gpu. A single cable with dual pcie power sockets would only use a single rail.
This may not be your issue but something to be aware of.
We will need more information, make and model of your PSU and it's age? On second thoughts, include yorus pecs like so:
CPU:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS:
Your psu has 2 x 12v rails with 30A on each. I know my old 780 recommended 42A on the 12v. To achieve this you would need to be using both rails which means 2 cables from the psu to the gpu. A single cable with dual pcie power sockets would only use a single rail.
This may not be your issue but something to be aware of.