Passengers are *way* more processor intensive than jetways and are more at risk of stuttering, due to the number of commands sent to the sim to play their animation, of multiple characters at time. Which is why we have a Passenger Density slider, since it might be needed.
The only thing fairly "heavy" of jetways, is they have 4K textures so, the first thing to try would be lowering the textures max size to 2K or even 1024 and see if improves things. If it does, you'll know your problem is the video card not keeping up with 4K textures. If you want to keep using 4K textures, lowering the ANTIALIASING quality might help instead.
If, instead, you don't see much change by lowering texture resolution, it means your problem might be related to CPU and, since our jetways are NOT, by ANY means, very much CPU intensive, there's clearly a problem with your setting, and I bet it's related to having changed the AffinityMask setting, and using a value which is not right for your system. If you added AffinityMask tweak, try to remove and go back to default, and see if it makes any difference.
