It is the cables that are making them stiff. Mine were the same way and i eneded up pulling the sides of the dash apart the removing the cables.
Then i stripped off the shitty old cable jacket and removed the solid inner wire and cleaned it. I got a bike cable kit from walmart for 4 bucks and clipped the end of the braided wire and took the new jacket. Sized it against the old one, timmed, then lubed up the old inner solid wire and put it into the new jacket. Refitted and now they are as smooth as silk.
A tedious job but better than buying new cables at 30 or so a pop and the same results.
I didnt do the third cable that goes down into the dash because i was lazy, just the two that go to the heater box