I'm sure any of these pickup autos can be freshened/enhanced to do whatever you want. Research it
Lack of power likely an issue... unlike 'modern vehicles' plenty of power
55mph sounds like highway. You still have to merge safely while towing, with that weak carb motor


oe frame, diff, etc seem robust enough
If you can't find a mitsu-specific bracket/hitch, it's very ez to adapt from another similar application.
A trip to the wrecking yard, with a tape measure, should do it