Ayyyy...no wonder people get confused. I am going through this process too, switching from a 1500 to a 2500 after buying a trailer that was "in the limits" by tv manufacturer website, but is overweight in the real world for the 1500. My advice since you already have the trailer.
1) Locate the TT Gross vehicle carrying weight on the yellow sticker on the side of the trailer. This is the max possible weight the trailer can hold.
2) Multiply this number by .15(15%) to get a tongue weight if the trailer was completely loaded. This amount should be used as the payload weight the trailer will add to your tv.
3) Before purchasing a tv, have it weighed to get its real world weight. This is where I went wrong. The manufacturer published weight of my truck was 4-500 lbs less then what my truck actually weighed on a scale. Best way to weigh is with all passengers and equipment in the truck that you will be using for camping along with full tank of fuel. Or you can estimate making sure to figure in weights for family members, equipment, and hitch.
4) Subtract the weighed number (or weighed plus estimated cargo) from the gross vehicle carrying weight of the truck that is printed on the inside of the driver's door of the tv. The difference is your remaining payload. If the number you figured in number 2 above is less than you should be ok, more than you should look for bigger truck.
I have a 6600 lbs dry weight trailer. TV gvcw was 6800 lbs. Published weight of my truck with full tank was 5400 lbs. Went one day with my kids and myself and weighed with half a tank and was topping 6000lbs. Once I added wife, hitch, and full fuel plus tongue weight I was looking at being 500lbs overweight. After months of avoiding the issue or looking for an easy way around it, decided the only way to fix the problem was move up in tv class.