Another food for thought on the Vision wheels. There has been one or more posts on the Vision wheels cracking around the lug nut hole. It appears Vision machined a relief at each hole (back side) to clear a brake drum clip. I do not know if this is true of all Vision wheels. I have not had mine off in years so I do not remember if mine have the relief or not. If I were to buy another Vision, I do not think one with the relief would be acceptable. To be fair, the cracking issue could simply due to improper torque. I do carry a torque wrench in my truck. With the special lug nuts, a special socket is required.
As I recall, you do not have limited slip (Anti-Spin Differential Rear Axle). If true, the only down side with a smaller rear tire would by load capacity.
The instructions (03-12 Dodge RAM 2500/3500 HD Long or Short Bed) on the install of your Super Hitch has a SHORT BED SPARE TIRE ADDENDUM. Among other things, it says "... the spare tire will stow away approximately 2”(5cm) lower than it’s original position." It makes no mention of reducing the diameter of the storage area. If you have not made the modification, we can do that. We can install your spare in the storage area, and see just how large of a diameter tire that will fit.
Personally, I am with kohldad and boogie_4wheel on this one.
Wayne