You may not have to worry about the 5er tow limit, but it's the pin weight that can cause the most problems.
Remember to subtract the weight of passengers and also the hitch (250 # ??) from the payload capacity, plus anything else you'll carry in the bed - such as maybe an auxiliary fuel tank (which I highly recommend), especially if your new truck will come with the small fuel tank (26 gallon ?) vs the larger one (35 gallon ?) .
And you'll want to base your pin weight on the GVWR of the 5th wheel (20%), not the empty weight.
