Where are you measuring the temps?
I have an older GQF cabinet 'bator. I have a digital thermometer in the hatching tray at the bottom, and a magnetic thermometer on the front of the top turner frame. I also use the metal thermometer that goes through the wall of the 'bator near the top. Each of my hatching trays has a metal thermometer (the kind that look like meat thermometers) in the center.
My temps are less than .3 degrees difference.
Do you have a clear window, or are you opening the door to the 'bator to read the temps?
I have a clear door on mine, so I can check all temps without opening the door.
Is something obstructing airflow from the fan? If there is something blocking the fan from circulating the warm air, that could cause a temp difference.
The only time I notice a significant difference in temp & humidity is when I have eggs hatching in the hatching tray at the bottom.
I have a sportsman as well and I have the same temp. difference. I have not yet had my bator full of eggs. Is yours?
I was thinking that when there are eggs on all the shelves the temp will stabilize just from the mass of the eggs.
The thermometer that turns the heater on and off is at the top and therefore the temp does shut off as soon as
it is warm enough up top and the air cools at it moves to the bottom.