amd radeon rx 580

Im having problems with my rx580 dropping frame rate at some restarts. It'll run good for one session then I'll shut it down and turn off the psu. Then after a few hours I'll come back start it and load up, and message appears that says wattman settings resetted due to system failure... I've ran...

Just to start off with some specs: CPU: Intel - Core i5-8600 3.1GHz 6-Core Processor Motherboard: Gigabyte - B360 AORUS GAMING 3 ATX LGA1151 Motherboard Memory: Team - Vulcan 16GB (2 x 8GB) DDR4-2400 Memory Video Card: GeForce GTX 1060 3GB ----> Now wanting to change to AMD Radeon RX580 8GB...