It may not be the thermostats, but their location. If your incubator is in the barn and there is a draft, the thermostats will react to the breeze. I bet in still air they all pretty much come in at 99 degrees plus or minus a degree. The biggest trick isnʻt whether its 99 or 101 degrees as much as its the SAME temperature constantly. Plus 50 - 60 % humidity and turning, of course.