it is not the lenghth it is the weight.  if you  are still liikng it is better to go with a fifth wheel.  they handle alot better.   also go for a set of air bags for your back end with tounge weight I get alot of bouncing and such with out my airbags. I canot remember the formula for figuring outtowing capacity but it is simple.   I would go into a dealer dodge type and ask them.