I do not have a Ram 2500 but a 3500. I am sure it weighs a bit more but no idea how much more. My 2022 3500 CTD, standard output with 68rfe trans, Crew Cab, Longhorn trim, 8ft bed around town for me is 16-18mpg depending on how much stop and go there is. Driving highway 65-70 it is around 19-20 have seen just over 21. Driving on the interstate at 80mph it is 18-19 mpg. The above is all above 6500 feet elevation and up to 10k elevation.
Adding weight in the bed does not effect mileage much at least at steady state driving ie highway. Throwing an empty trailer into the mix almost regardless of trailer type ie 10' utility with standup wire mesh ramp (1200lb weight), 18' flat bed equipment with stand up ramps (4000lb empty weight) or 12' dump trailer (about 3000lbs) it drops down to about 15-17 on highway, throw on a 9000lb tracked skid steer and its 15 mpg at 65mpg. Throw the fifth wheel on and it drops to 12-13 sometimes below 12 but I have never seen below 11. That dang air resistance seems to come into play immediately but the fifth wheel really takes its toll aerodynamically speaking.
The only one that surprises me is the small utility trailer. Every time I pull it is usually sporting a can am ATV at about 900lbs and get 15-16mpg not much better at all than the other ones empty at twice the weight and only a little bit better then when I am hauling the equipment trailer with the skid steer on it. And that combo weights more than my fifth wheel by 3000lbs (13k vs 10k).
The truck has no issue pulling any of them at all. I never have a stressful drive or think the engine is working that hard. My only stress pulling any of my trailers is other drivers doing stupid stuff. It just chugs along like the weight is no problem for the engine.