Just purchased a 2013 1500 Silverado 4WD EXT CAB LT. One of the options is the Z71 off road suspension package. It says off road skid plates, high capacity air cleaner. I thought the Z71 would have Rancho shocks as the 2013 sales book describes. Supposedly I have gas shocks on the truck but not the Rancho shocks. Thought they all had the Rancho shocks with the Z71 off road suspension. Any ideas.