the M5OD is fine for light-duty use, but not for heavy use. in general, it is a light-duty gearbox, and as a result is more prone to various failures when subjected to heavy use such as towing, overloading, or abusive driving.
the other major annoyance of the mazdog is the excessively high gear ratio on reverse.
for a gently used highway vehicle, its a good unit and will last a long time, but its not suited for heavy use.
83 F250 flatbed 300-6, NP435, 4X4, 5800lbs empty weight
87 E-350 6.9 diesel, c6, 3.55s, powertrax no-slip locker, onboard 120v power and compressed air, built out with toolboxes and toys