You might want to figure out why it's so hard to move in the first place. Unhook the cable from the valve on the firewall, see if the control moves easy. If so, then it's the valve that's sticking. Or unhook the cable at the end inside the car. Maybe the cable is kinked so it doesn't slide nicely. Dont replace the parts that aren't broke.

PS for Mountain...
Below the glovebox that isn't a valve. It's a crank or lever that pulls & pushes the cable. The actual valve is at the other end of the cable, under the hood, sorta below the fuel filter.