Help with rear self leveling suspension

[Joyaant911]

How do I know change out my rear self leveling? Is it a normal shock that I purchase or what? Can't find anything online this is my first truck. Also what are the symptoms of my rear suspension going back? In the mornings my rear is pretty low but once car is turned on it raises bAck up.. Lately my truck has been makin a noise in the rear when going over bumps and it's becoming more frequent and annoying I'm wondering if this is related to the rear suspension maybe going bad. Any suggestions truck has 100k