Old-Biscuit is right, you can't change the capacity rating. Adding springs or air bags will help keep the truck level.
Your payload is limited, due to the heavy diesel, and the 10,000 lb GVWR. IMO, your truck is capable of handling those FWs. Yes, you may need some suspension enhancement.
I would always want to be able to fill my fresh water tank, and not worry about it, so I would not subtract that wt.
Your truck is more capable than some of the numbers indicate IMO, but still your decision.
Your combined rating is higher than you posted. My 6.2 gas is rated for 19,300.
Jerry
