I think you'll find that the tradesman has the 6000 RAWR because of the 245/75/17" tires. They only have a 3000lb rating. Move up to an SLT or higher and you'll get 6195lbs for RAWR. That's the way my 12 2500 is. Ram has changed their tow capacity site in the PDF. They no longer break down ratings buy model, just cab/bed/drive train conf.
Either way putting over 3000lbs in the bed of the Ram 2500 is asking a bunch. Even with upgraded tires. Why not just spend the extra $8-900.00 for the 3500? Costs $350-400 for bags and certainly more for upgraded tires.