Low GPU usage in fortnite, causes low frame rate

[eyalm2004]

I have an i5 - 8500, gtx 1070 (g1 gaming), 8gb of ram (soon upgrading to 16), and an asus h310 prime. in fortnite,i can get 120 fps on 1440p on custom settings and get around 50%-70% GPU usage, now i get some times even 60-70 fps, and my gpu usage drops to about 40%-50%, now i have tries a lot of things: high performance mode in windows,reinstall drivers, resetting my pc, reinstalling fortnite, and nothing works. please help!

 

[Ralston18]

Additional details needed:

What version of Windows?

What drives are installed?

PSU: make, model, wattage, age, condition?

 

[eyalm2004]

windows 10, latest version
nvidia's 416.34 (latest)
PSU: not sure what model,but its corsair, got it 4 months ago, i think its 600/650/700 wats but im not sure

 

[eyalm2004]

Additional details needed:

What version of Windows?

What drives are installed?

PSU: make, model, wattage, age, condition?

windows 10, latest version
nvidia's 416.34 (latest)
PSU: not sure what model,but its corsair, got it 4 months ago, i think its 600/650/700 wats but im not sure