Bump steer is mainly a geometry issue. How much angle do you have on the draglink? The more angle the draglink is at, the more bump steer you will have. Why? Because, when the suspension compresses, the draglink angle is reduced, but since it's length stays the same, that will cause it to "push" against the passenger side steering arm, inducing a right turn to the front wheels.

Could also be other items, such as the steering alignment being off, get the caster angle and toe-in checked and corrected if necessary: http://www.4crawler.com/4x4/4R_TechInfo.shtml#Steering

Also, could be worn spring/shackle bushings or even just wide wheels and tires, especially if you are running very low backspace on the wheels (spacers, etc.). A steering stabilizer could help, at least worht a try:

http://www.4crawler.com/4x4/CheapTricks/CrossoverSteering/index.shtml#SteeringStabilizer