[MPaulHolmes]

At 12v and 40 amps continuous motor amps (2 mosfets are installed out of the 12) the bus bar they are soldered to stays really cold, and the TVS diode temperature climbed really slowly, and then found its equilibrium 5 degrees above the temperature it started at. That could be the result of the spike on the gate exceeding 15v, allowing a bit of current to go through the TVS diode, or it could just be that it's above the bus bar, which probably warmed a couple degrees.

Now I'll see if the temperature of the TVS increases more at higher power section voltages.

EDIT: The TVS temperature climbs slowly even when the gate is well below the clamping voltage.