been through this many times! these newer trucks are quite a bit higher than the previous ones, with deeper boxes to boot! which put is in a horrible situation MOST times. We got lucky with our 2013 Laredo and it was essentially perfectly level for my 2012 duramax dually.
Having said that I had to lift our previous triple E topaz luxury edition to make it level. It would surprise you just how much lift you will need to make it sit level with your truck, I would think your looking at, atleast 6" of lift to get it close. As far as I am concerned you should have AS MUCH bed rail clearance as possible, were sitting at 9" of clearance right now and its still touch and go at times. Youll have to have a weld shop make up a sub frame for you and then have the axles re-mounted to it. Being a welder I did my own on our triple E, used 2" x 6" x 3/16" thick rectangular tubing welded directly to the flange of the existing frame I-beam, with 2"x2"x1/4" square tubing cross members in an X configuration to prevent twisting/flex.
Its just my personal preference but I am an absolute freak when it comes to towing level, ill spend hours tweaking to make sure its as close as humanly possible, that goes for the boat on behind the camper too!