No, its not the Z71 package. Z71 on the 2500HDs consists of Rancho shocks, skid plates, and a G80 rear locker and that's it... There is no front springs on these trucks as they all use torsion bars. Only 3500HDs get an extra rear leaf spring.
More than likely the reason the ride on the 2013 was so harsh is the previous owner attempted to level the truck by cranking the torsion bar keys (very common). Without putting on longer shocks to compensate for the extra travel the ride will go to******in a hurry. Turning the torsion keys back down will correct the problem and return the stock ride.