Lets ask what you actually have? Someone mentioned a dually, but is it??? This is the most important question, as I did not read that you had a dually in your original post.
ST, SLT, Larimie, longhorn? (There are some small differences as options change max weight somewhat. no big deal..)
It dont matter you have air bags or not. It dont change anything regarding what you can tow......
Whats the actual make and model of 5th wheel, just for our reference???
Once you give us this info owe can help... Or look here and figure it out...
http://www.dodge.com/bodybuilder/2011/docs/ram/rammlup3500.pdf
And if it is a dually, and you get the gear change dont forget the biggest A55 trans cooler you can fit...
All else you should be fine except for some white knuckles and an empty wallet on fuel economy...:)....