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

[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