Transmission cooler help

What else changed? Simply adding a cooler alone shouldn’t cause it to run hotter no matter where it is. Too small of a connection tube or hose? A kink in the line causing slowdown of fluid? Was cooler used-possible internal blockage?
Did you bypass the original in the radiator? If so, new unit might be too small.
10 Degrees isn’t much, so it wouldn’t take much of a fluid slow down. Obviously a full kink would seriously impact flow and cause more than a 10° rise.