Looking at purchasing a new Freightliner Cascadia day cab, Detroit with auto shift, twin screw, noting fancy. It will become a 40-42 foot unit, 18 ft garage, 22-24 foot living. Mostly to visit family across the county. What would be the best rear ratio for cruising about 75 with this unit. I plan on carrying a Toyota Rav or Honda CRV in the garage, still should not be over 50k loaded.