just a couple of thoughts...
1.You have three machines from different manufacturers with quite different looking thermostats.
They are all giving the same temperature when set to 375. I wonder if it is your thermometer that is wrong? maybe they are all giving 375 and your thermometer is under-reading? I have two milk thermometers for making espresso coffee. they do not agree, nowhere near it. I recently also bought an oven thermometer, I noticed in the stores that some of the cheap ones, there were several hanging on the display and they were showing different temperatures despite measuring the exact same temperature.
2.They probably all have a sensor probe for the thermostat. Check that it isn't touching the heating element, that will mean the probe is being heated directly by the heating element instead of purely measuring the oil temperature. (This would trick the thermostat into cutting off too early.) I used to cook for a living and for a few years we had a small two-pan benchtop commercial fryer. In that we had to check that the probe wasn't touching, it was held by stainless steel clips next to the element and could touch if it was sitting wrong - easily bumped during cleaning.