What kind of thermostats are you using? I had a similar problem when using a normal on/off thermostat with a CHE. I'd set it to what temp I wanted, thermostat would let it get there and turn off, but because CHEs stay hot for awhile with no power the temp would always still get a little higher than I wanted. I compensated for this by just turning down the temp it was set to.

What could be happening is your heatpad is getting where it needs to be, the thermostat turns off, but the surface is still hot, the pad is still hot even without power while it cools down as you mentioned. Are you keeping in a glass or PVC enclosure?

Of course it could also be faulty equipment. The good news is, at those temps you're probably not going to hurt your snake, BUT it's good that you're paying attention because if there's something faulty with the thermostat you could overheat to the point of injuring your animal.