low gpu and cpu usage low fps

[snapcrackpop]

so i have a rtx 2070 and a i7 8700 however in csgo at the menu i get 780fps or more with 20% ish cpu usage and 55% gpu however in game i am using around 25 to 35% cpu and 40 to 50ish gpu and im only getting a unstable fps the goes from 80 to 150 ish fpswhy is this happening i did set a launch option for unlimted fps but that doesnt seem to help i also tryed g sync on and off no diffrence and i set max performance to in nivida control pannel 

[SenKa]

Are your settings all the way up? I've had this issue with Source games to where if the settings are too low for the hardware (and thus FPS is through the roof) it would exceed that of the engines capabilities and freak out.