I noticed that my GPU hits 75 degrees when playing. Should it be going that high? Frostpunk doesn't seem that graphically demanding, so I don't know why it would affect the GPU that much.

This game will run my GPU up to 190* F if I dont have my case fans set to high. It may not look like it, but this game IS demanding on your GPU.

It does not ignore Vsync settings however there's a lot of particles, especially smoke, in the later part of the game that is quite taxing. Try reduce particles quality in graphics settings, and shadows / global illumination if that isn't enough.