Current setup
Asus rog B450F Gaming MB
AMD Ryzen 5 2600 *
Corsair Vengeance LPX DDR4 3200 C16 16gb
Asus rog strix RX 580 gpu*
Ultra x4 750w psu
**
I purchased an Asus Rog Strix RX5700 XT OC
I uninstalled the Amd Radeon software, removed the RX 580, installed the RX 5700,
plugged one 6 pin to the 6 pin psu and to Gpu with a 6 pin to 8 pin adapter, and plugged in a 8 pin pcie to the 8 pin psu and 8 pin gpu.
I download the new Radeon software, installed, restarted, and brought up a game.
I also run gpu tweak to monitor. Once in game, it was unplayable due to the lag spikes, the gpu spikes in game coincided with the spikes I noticed while monitoring GPU Tweak.
GPU Tweak would show that the GPU Clock and Memory clock would spike from max to minimum.
The graph on gpu tweak would never stay solid.
*After getting fed up with it, I uninstalled the RX5700 and reinstalled the RX 580, restarted game and everything ran fine, gpu tweak monitor would stay solid during game play.

Is this a CPU Bottleneck or psu issue?

I looked at specs of the rx5700 and it says 1 6+2 pcie and 1 8 pcie

Note, I ran the asus benchmark and the GPU usage was always 0

I appreciate all your help*