Cargo capacity is key for a 5w. Assume 20% HW for a given trailer. If you want to tow a 16K trailer, you need 3200 lbs of payload/cargo for the trailer, add in another 500-700 lbs for a couple, hitch, Mr Winston the lap doggy! and other assorted odds and ends in truck.......If you need 25% hw, make that 4000 lbs of payload plus the 500-700 lbs. Yeah it may be rated per say, but if you do not have the payload, your screwed!
So it would not surprise me a sw 2500 is down around 8-12K lbs. My old 96 CC with a 9200 gvwr, by the time I added in 2 adults, 4 adult sized teens, rack, canoe, cross bed tool box. I had all of 600-900 lbs of payload left! not a heck of a lot of 5w. ie 4000 lbs. or 8k if I went ball mount at 10-15% hw needed.
Marty