Well for once I would say the salesman is probably correct. 12k# unloaded is likely over 14k# GVWR meaning aweful close to that 3000# pin wieght without anything else (like hitch, full fuel and passengers)in the truck. Not only will you likely be underpowered but probably over the carrying capacity of that truck in real life
>14k# GVWR is squarely in dually territory. I pull a 12k GVWR (and scaled) FW several thousand miles a year. I use a dually and wouldn't use anything less
For your truck you should be looking for around 10k empty (12k GVWR) maximum would be my guess.
