I see you got the same truck I do, but you have an extra rear tires.

These have 60K miles on them, 1/2 the time loaded. Energy Suspension. might cost $35.00 per side. I can look up the part number if you need it. uses factory bolt hole.
What happens as truck weight drops, these blocks cause the helper spring (on top of the 2006 dodge spring pack) to hit the frame perches sooner. Less drop before the extra springs kick in.
It also cushions that transition where you are loaded, you hit a bump and the helper springs crash into perches with a jolt you feel all the way up though the truck into your back.
Been towing a 10K 5th wheel since truck was new. Now also have a 3K TC. Truck still sits 1" higher in rear than front with TC loaded.