Basic Truck / Towing Edumatcation
Forget so-called "trailer tow ratings" and forget about your truck's stated payload capacity, both are nebulous, even if based on the newer J2807 tow standard that many manufacturers are now adopting. :R Instead, go weigh your truck with a full tank of gas and weight distribution mounted, even throw the spring bars in the back. If you yet don't have a weight distribution system allow 100 lbs for it in your calculations. Once weighed subtract your weight from the scaled weight, assuming you were in the truck at the time it was weighed ... the result is what your particular truck actually weighs as it sits there with a full tank of gas, ready to be hitched to a trailer. Subtract that number from the truck's stated GVWR and the result will be your particular truck's actual payload capacity, not some fanciful number the mfg has assigned to it. Payload capacity is what you'll use to account for the weight of everyone and everything added to the truck, including any tongue weight transferred from the trailer to the truck. Exceed this real world payload capacity and you're sure to exceed it's Gross Rear Axle Rating and despite what the pundits may say this is a situation you want to avoid. Sure, your truck will tow a larger trailer but so too can a lawn tractor ... but can it do it safely within all the various manufacturer ratings? :p