Are you replacing with standard mono tube shocks ? Unless you are replacing with high end reservoir shocks I would suggest the standard length of shock for your truck. Unless your truck has a small lift installed.
Mono tubed shocks are valved for specific rebound and compression strokes. Some has slight adjustments to them but not much. Unless you are buying higher end mono tube ( or even twin tube as sometimes referred too ), or reservoir shocks that can be adjustable for ride quality, I would stick with what your truck calls for.