First off.....
that pin weight is DRY (unloaded) weight number.
WET pin will be closer to 1400#
Best changes to 150/1500 for towing....upgrading to at least a 250/2500 for 5th wheel
Payload is the issue.
Payload includes ALL passengers weight, any stuff in cab, any stuff in bed including that 5th wheel hitch PLUS the wet pin
1400# eats up a lot of payload for a 1500 especially a 2003 4x4 which only has 1200-1300# payload to begin with.
Then you have the RAWR which is 3900#
Curb weight is roughly 3100# leaving only 800# before exceeding RAWR.
Air bags do NOT add capacity.