How to improve towing for 2007 Chevy 2500 HD Duramax

Hi, I own a 2007 Chevy Classic, 2500 HD Allison Duramax, 6.6L V8 Turbo, with full tow package, 3.73 rear axel ratio, short bed, extended cab - towing capacity for a 5th wheel/gooseneck is 15,400lb. I...