To better figure out what's causing the issue, please post a log. I'd also recommend keeping an eye on task manager to see if it's your graphics card or your CPU that can't keep up.
To make a clean log file, first restart OBS, then start your stream/recording for ~30 seconds and stop it again. Make sure you replicate any issues as best you can, which means having any games/apps open and captured, etc. When you're done select Help > Log Files > Upload Current Log File. Copy the URL and paste it here.