I have ordered 5 Method NV/HD wheels and 5 Nitto 305x65r18 Ridge Grapplers a 12 ply "F" rating more than enough for the 6,500 lbs. on the rear axle. Because this tire/wheel will be about 5.75" positive from hub mount surface, I installed 3.5" Bushwhacker pocket fender flares to cover them. At the rear I'll have no stick out issue because the Tiger coach body is more than wide enough to cover. FYI, my 3500 has the snow plow prep pkg. I'm told without a 500 lb. plow, the front sets a little higher than normal with more tire clearance. By my measurements, my new 33.6 tall tires are going to be a close fit on front. No problem at bumper because I have a Aluminess bumper. The rear of the front tire is going to be very close to the cab fenderwell. I dought I could run 35" tires without a lift kit. Lifting is not a good idea for my tall chassis mounted Tiger RV coach.
I did not like 19.5 tires for many reasons stated in post #6. Not to mention their low 65/75 MPH speed rating. On the interstate I run 75/80 often. Anyway IMO, if you are going to typically be carrying more than 4 tons! on your 3500. You need a 4500/5500 truck. I feel my truck is safe at 11,300 lbs. but at it's factory limits.