Hi RCULVER,
You didn't mention the Bighorn model #, so this answer is approximate.
You should ignore the pin weight spec on the Heartland website and instead plan on a loaded pin weight of about 20% of the Bighorn GVWR. Most Bighorns have a GVWR of 15-16,000 lbs. That would give you a likely pin weight of 3,000 to 3,200 lbs.
When you consider how much pin weight is ok, you're looking at the truck payload spec - for your actual vehicle - not for the best case in the manufacturer's brochure. The payload is usually found on a label inside the driver's door. The payload has to carry the pin weight, plus weight of your hitch, bed liner, bed cover, tools, firewood, pets, passengers, and anything else in the truck.
It wouldn't be surprising to find you're 1,000 lbs over the payload spec.
You might want to spent a little time visiting
Fifth Wheel Safe Towing. It's a website designed to help you work through to a more specific answer.