From what I have seen, problems usually tend to be three things on driver's seat heater issues:
1) Blown fuse.
2) The paper thin heating element in the pads tear.
3) Bad switch.
The the most frequent to happen is torn elements in the pads. Looking at how many times someone has planted hopped on and off the driver's seat cushions... It would not surprise me, if that happened.
Replacing the heater pads is not hard to do, from watching others tackle the job on YouTube. But, I believe you need to remove the seat from the truck to get seat covers off and access the heater pads sitting between the seat cover and the cushion.