I had supplemental air springs on a previous truck for when I was towing and hauling heavier payloads.
Something along the lines of this:
Air Lift 57275 LoadLifter 5000 Series Rear Air Spring Kit https://www.amazon.com/dp/B000CFQ2XM/ref=cm_sw_r_cp_api_i_WB39SQE9FQ782MKBTY5A