The site for finding trailer tow maximum is here.
https://www.ramtrucks.com/towing/towing-guide.html#/landing/bytowing/search/
The following is long, and a combination of real and theoretical numbers to show how loading weights isn't a simple thing, and only fully loading and then measuring at a CAT scale will give you full information needed to know if you are within specs or not. Don't use my numbers as a rule of thumb, as I said they are not technically correct but just to help visualize things.
With my 2500, I have 3,000 payload capacity and 12,500 trailer towing capacity. Assuming a 60/40 front/rear split for vehicle, my center of gravity is nearer the front when full of fluids and devoid people and stuff. This would have about 4300 pounds on front axle and 2700 on rear. As I add weight two of the things that impact cog are obviously where new weight is put (usually behind base cog) and height of weight added. Since the bed is naturally where a lot is added, that shifts cog back a bit. Then a travel trailer and hitch really shift cog back even further. So it is possible that the if the tongue weight of a trailer + hitch (say 1500 pounds total) results in a larger added total weight measured at the rear axle than just the total of the payload added. So say maybe that 1500 plus 10% of GVW (7,000 from above) shifting from front to back axle changing total of rear not just 2700 +1500, but 3400 + 1500 = 4900. This is just for example and not exactly how the math goes, but idea is there. If I max my weight to 2500 in bed plus 500 pounds people in cab, I could have shift of cog with numbers being 15% moved to rear, 3750 + 3000 payload = 6750 gawr rear or 250 pounds over even though I am within total payload capacity.