If you don't have a mechanical issue with the axles, or alignment, the best thing to do would be to go to 16" wheels/tires. I think they are optional now, when we bought ours, an 07 4012, it only came with 15"wheels/tires. I had the dealer replace all of them with 16" aluminum wheels and Michelin tires, have not had a SINGLE tire or wheel issue since it drove off the lot, and it's been in some nasty places, and we haul down the road, pulling with a semi. Technically, the 15s fit the bill for weight rating (we're all under the weight limit right?), but there is a reason 16s are an option now.
-JR