Code P0128

I have a 2003 CE model with just 170, 681 miles on it. I changed the radiator, thermostat, & temperature sensor at 169,556 miles after I had over heated it. I got a check engine light that's giving me code P0128 which I've attached a picture of it. The thermostat and sensor are new so I don't know how it could be failing. The only thing I can think of is that I burned the head gasket when it over heated and it's causing combustion to either make the temperature sensor get a bad reading or damage the thermostat. The problem with that though is that I'm not getting white smoke out of the tail pipe and I'm not getting milky oil. When I turn on the engine with the the radiator cap off I do get bubbles sometimes though. It seems weird that a new thermostat and or a temperature sensor would already start failing. I suspect it's the head gasket. What do you think?