A steering damper (stabilizer) is more or less a shock absorber. They mount to the tie rod and the axle/frame, depending on suspesion type. The main purpose is to help control bump steer by dampening the road shock. Not really a necessity for a stock truck, but can help on trucks that see alot of rough roads and/or have oversize tires. especially if there isn't any type of power assist on the steering.
As far as control issues, having the alignment angles (particularly the toe setting) correct and the tires inflated to the correct pressure will correct virtually all handling problems.
This is what a stabilizer looks like installed.
http://rides.webshots.com/photo/2467856270092261295gWlAJo
