I also have a 2013 Ram 2500 and found it caused my RV to ride a bit nose high. I was able to lower the rear of the truck about an inch and a quarter by removing the spacer blocks that sit between the under side of the rear springs and the axle. The blocks were then placed on top of the springs, so the U-bolts were still the correct length.
I made this same modification to my '04 Ram, and found that Dodge is still using the exact same setup with the new trucks that they used in '04. I believe I read about this modification on this or another RV forum. It helped level out my fifth wheel when towing.
This is not a particularly difficult change to make, although you'll have to come up with a solid, safe way of blocking up the frame when you remove the U-bolts and lower the axle. Just do one side at a time, of course. That way, the other spring will hold the axle in place.