As a medic for 40+ years and having driven such vehicles, and having been responsible for coordinating maintenance… couple things:
These vehicles have been driven very hard. A lot of cold start, pedal to the metal by those who don’t pay the bills: trans care and drivetrain issues should be closely evaluated
These vehicles usually receive regular preventative maintenance that often POV don’t get: oil changes, belts and hoses are typically replaced on a schedule.
The electrical systems are hard pressed in service. Extra lights and sirens, heaters and portable equipment chargers place constant stress on electrical components.: check all your grounds and connectors for corrosion and loose connections. There is usually an auxiliary circuit board with relays and fuses/breakers, make sure all ends are secured and no live wires are just bantering about. Might even be best to terminate and circuit not in use at the relay; less chance for a short.
Most of the vehicles we’ve sold off went on to live a long post-service life, I’m sure yours will as well.
Best of luck