old GPU issues on new hardware

Jan 6, 2019
I have upgraded my motherboard, CPU, PSU, RAM and liquid cooling but running an old GPU, specs of new gear are below;

MB: Asus ROG Maximus X Formula
CPU: i7-8700K LGA1151
RAM: G.Skill DDR-3200 16GB
PSU: Corsair HX850i

The GPU is a: NVIDIA GeForce GTX 680

My issue is when I am using the PC it has no issues, but when I start playing games (mostly WOW) the fans rev up and the FPS is really laggy and it sometimes crashes at the worst times. I get no error messages and I have done a RAM test with no issues, I am thinking its the GPU cause its old I have also lowered the graphics settings in the game but it makes no difference. The FPS also jumps around a lot and when I was running my previous system I had no issues.

Also running Windows 10 I didn't do a reinstall it just updated everything on its own, and all the drivers are up to date.

Please help thanks.