Code P0128- Should I change Thermostat?

Ive been getting the P0128 code on and off now for about 2 months and I finally decided to try to change the thermostat myself. This seems like a huge pain in the butt for all the things youd have to remove to get to that thermostat. My truck is a v6 4.3 L and has 79000 miles and has no other problems besides the AC blowing hot air anytime you select hot air, even if you go back to cold air it still blows hot air.

thermostat shouldn't be that hard to get to. but yes, it sounds as if the thermostat is not working correctly anymore. as for the heat issue, not knowing the year and type of controls is a bit daunting to help with, but if it is like my S-10 with manual controls, the hot/cold air door is actuated by a little actuator motor. this could be sticking a bit. some people have taken theirs apart and cleaned and lubed them up, but would say better off replaceing if turns out to be problem.