Med Duty tow rig questions

I'm looking at retiring in the next 5 years or so and I'm just starting to look at possibly using a medium duty rig to tow a custom built toy hauler that has yet to be built. The 5th wheel that I'm thinking of having built will be in the 35' range and have the capability of hauling my restored, mostly stock 1980 FJ40 Land Cruiser that is exactly 2 tons. I am looking at something like an International 4700 Lo Pro type of tow rig. I want the Allison auto so the wife can drive so in an emergency situation. What engine make and HP level should I be looking for to get decent power and fuel economy? What rear end ratio is best for pulling and fuel economy? Any particular outfits I should stay away from and why?

Thanks for all your help in advance.

Randy