re: "The temperature has been verified..."

You've done everything that makes sense and it should be fixed, but because it isn't I'd like to know how the overheating temperature was verified.
Was it by a shop that was, by any chance, looking forward to your business? Or did you verify it yourself?
If so, how did you do it?

The reason for asking is that, 95 out of a hundred times (especially if you've done all that and have no improvement) you're actually chasing a phantom known as the Temperature Compensation Board. This is not a temperature sensor! It's a circuit board that overlays the temperature gauge behind the instrument cluster. There's a simple bypass, where you remove the board and insert the two ends of a wire (a jumper) to let the gauge become accurate, like in all pre'85 cars. In '85 they introduced the TCB, and that often fails with false and weird temperature indications -- I've had that happen in both of my '93s.

So you need to verify the coolant temperature -- get an infra-red (remote sensing) thermometer (they're are a lot out there) and just aim the laser aiming beam at the metal cover of the thermostat housing. That will be the true coolant temperature. Then you can go from that point.

Good luck.