Variable Matlab speed/performance

Hello

I'm running complex code (100 files in path, all of them needed) that implements a real-time GUI using a timer. I've noticed that the speed or performance of the code varies enormously: the time to complete a step can be as low as 60 ms and as high as 150 ms. Any idea what can cause this kind of variability?

I have a good computer (i7, Nvidia 1060, 16 GB RAM) and task manager says I'm only using ~25% of CPU power, 41% of memory, and 4% of GPU. I'm using Image Acquisition and Image Processing Toolboxes. I don't have any big programs running other than Matlab. Often, simply restarting Matlab or Windows will change the speed of my code. What's going on?

Chris