The Fox shocks can be valved, by fox or anywhere that services shocks, for any rebound & dampening you desire. How you valve them all depends on your needs. Most people just run em as they were out of the box. The perfect valving for street, track & offroad are all different so if it's a multi use truck it's about finding a happy medium. I'm not nearly as familiar with Bilsteins so I can't remember if the 5100's are a serviceable shock.