Planning on buying a 2008/09 2500 HD Duramax 4x4 SRW. Will also be buying a BigHorn 5th Wheel. Would like to put 285's on truck, guess my question is, is about a 2" lift going to cause problems in towing the 5th wheel?

On the Bighorn model, the axle shackles are not listed as being adjustable. I just bought a new 2009 Cyclone Toy Hauler from Heartland which does have the adjustable shackles to adjust for pickup height. You would have to have a hitch that can drop in height to accomodate the extra height of the truck. That will decrease the distance between your bedrails and the bottom of the coach.

A lifted truck, or one with taller tires, will cause the nose of the Bighorn to run high, transferring the weight to the rear axle and possibly overloading it. The tires will also change the year end ratio which will make it harder on the transmission, etc. Stock tires and height are best for towing and the closer you get to your GCWR the more important it is to stay stock. I have a Landmark from Heartland, a little heavier than most of the Bighorns, and I'm maxed out and my truck is stock.