Adding a leaf to my leaf springs

[quick83]

I have a 2014 Sierra With 7000 lb axles. We had 2 flat leaf springs on the passenger side. I had all 4 replaced with the correct ones for my axles and weight. With the rv empty the passenger side still sags some and the leaf springs on that side still look flatter than they should. I’ve heard a lot large fifth wheels can have this issue. Has anyone added a leaf to the springs on the passenger side to alleviate this issue? Also Any ideas on the cause of this. Just wondering if they will quickly get worse again .