OOOOK. After the Control board swap yielded the same results, I used a cloth to clog up the un-damped slot between the FZ/FF bulkhead. It passes between the Evap box and the top of the fridge. With that clogged, the fridge descended to the set temp and the damper began opening as needed to control temp. The freezer still seems to work a bit harder than I imagined to keep cool, so you are right on with the insulation kit tip. The freezer is also not stocked up, so perhaps that will help it hold temp.
What is that slot supposed to function as? Air return?