Try using a bitrate of 3500 and test which server is the best in your area by downloading this >
https://r1ch.net/projects/twitchtest
Usually OBS uses the best and closest server in your area but you can test the maximum upload speed & fastest server on that website.
I am guessing that your using x264 instead of the Nvidia Encoder ( nvenc ).
If so what is the quality preset at? ( Low, Medium, Fast, Faster, Superfast, Ultrafast? )
The higher the lower the cpu load.
The bits your uploading goas through your cpu so try to go from ultrafast and if that works well with no frame loss then go lower until you found the right settings.
Also what worked for me was to change the process priority to Above Norma (Higher could affect gameplay).
View attachment 40679
If this didnt help try to update your network adapters via Device Manager.
Let me know if anything helped.