71 demon heater controls stiffness!

Spray some lube into the cable tube and work the wire in and out over and over. Keep going at it from both sides until you're sure the entire cable is lubed up. It should move freely at that point. Then just ensure that the cables aren't taking a route where they are bent too tight when you reinstall them.

I wouldn't try and force the control sliders over if the cable is too stiff. You run the risk of bending the wire and potentially ruining the whole cable.