If your rear suspension is bottoming out with hard hits then it's time to replace your sagging springs with new or add some spring spacers back there. Two must checks/replace are lower ball joints and radiator. If you don't know when the lower ball joints were replaced last or they look damaged/old then replace them now before they fail and cause a lot of damage. OEM is the general recommendation for replacement lower ball joints, and make sure to get the lower ball joint bolts as well. If the radiator is brown/cracking/generally old looking then it would be a good idea to replace it before the transmission cooler in the radiator fails causing coolant and transmission fluid to mix causing transmission failure in 99% of vehicles that this happens to.