WOW... I must have hit a nerve or something.
Could be just your gauge, I have an Isspro gauge and a Scan gauge, they both read pretty much the same for all conditions. Of course Isspro uses a quicker reacting probe as well.
Your comparing a sensor that is buried inside the tranny to one that is typically installed in the pressure port... One is subject to air temp changes, heat of the metal around it and the flow of the fluid.
There is no issue with a tranny temp in the port, it reacts plenty fast enough.