Your current Duravis LT tires are good tires but are not rated to carry the load of your new rig. As stated above you can negotiate to a larger wheel/rim and better tire, it will no doubt lead to a higher price out the door, but will be less than doing the upgrade later in most cases.
Depending on how much you plan to travel the first couple of year you could stick with the Westlake tires for awhile and make a decision later down the road. They are rated for 4K# and should give decent service for a few thousand miles as long as they are cared for and aired up to max psi.