75 FPS to start, 25 FPS after respawn, until switch to desktop and back

[hipifreq]

Here's my specs, it's a new machine I assembled recently:
ASRock Z170 Pro4s mobo
Core i3 6100
MSI GTX 660 gaming 2GB
8 GB DDR4 3200 (2x4 GB)
120 GB SSD
Win 10 x64 Pro
All the latest stable drivers for the mobo and GPU and no OC.

When I fire up PS2 at high settings I get 75 FPS even in moderate to heavy fights. Both CPU and GPU temps look great the whole time. When I die and redeploy, after the loading screen, my FPS drops to about 25 and everything looks like low settings. However, if I Ctrl-tab to the desktop and back I get solid 75 FPS until the next loading screen hits.

has anyone else seen this issue, and perhaps straightened it out?
Other games seem to operate just fine.

[AUGRaijin]

Your issue here is your CPU is Bottlenecking, its Cache is not releasing or refreshing and when it fills up its stuttering by power cycling to desktop your forcing the Cache to refresh

did you build this PC or buy it this way?

to fix this issue step up to an I5 or an I7 cpu

the only other issue i could possibly foresee is that if you built this pc, did you make certain your ram was placed in their correct slots for Quad Channel optimization, meaning since you have 2 sticks of ram does your motherboard have 4 dimm slots and if so are your ram sticks placed in dimm1 and dimm3 or dimm2 and dimm4 instead of dimm1 and dimm2 and dimm3 and dimm4 being combined quad channel ram uses paired slots to run quad channel ram in offset ram slots often separated by another channel where as ddr3 would use sequential ram slots in sequence...for example DDR3 would go by 1-2-3-4

ddr4 would use
1-3-2-4

1-3 for ......................................channel 1
2-4 for ......................................channel 2