I just looked up the 2009 Dodge 2500 and 3500 towing specs, and looks like their numbers are higher than those of the GM trucks. (what's up with that, GM?)
The Ram 2500 has a published payload capacity of 3,650 lbs, while the Ram 3500 has a payload capacity of "up to" 5,130 lbs (it doesn't say whether this is for the SRW or the DRW, but my guess is that this is for the dually).
Therefore, doing the math again:
Ram 2500 payload capacity: 3,650 lbs.
Typical fifth wheel hitch weight: ~ 200 lbs.
Typical tank of diesel fuel: ~ 250 lbs.
People (2 adults x 175 lbs): ~ 350 lbs.
Likely installed options: ~ 100 lbs.
Total remaining payload capacity for pin (3650 - 200 - 250 - 350 - 100): 2,750 lbs.
Therefore, if you have a 2009 Ram 2500, and you only have two adults, you can probably handle the smaller Bighorns such as the 3055RL, assuming you don't load the trailer right up to its 14,000 lbs GVWR.
Hope this helps.
Cheers,
Chris