You're probably thinking correctly. It's not the towing capacity but, rather, the pin weight of the loaded trailer on the rear axle of a 3/4 ton truck. Take 23% of the GVWR of the trailer and use that as the loaded pin weight for estimations. Scale your truck with fuel, passengers, hitch, and all your stuff and subtract the actual weight of the rear axle from the GVWRR (gross vehicle weight rating rear) on the truck's door sticker. You'll most likely be in the danger zone.
Rob
U.S. Army retired
2020 Solitude 310GK-R
MORryde IS, disc brakes, solar, DP windows
(Previously in a Reflection 337RLS)
2012 F350 CC DRW Lariat 6.7
Full-time since 8/2015