As a former hose dragger here... It would be plated as a heavy-duty truck (need a DZ to drive it in Ontario)
The sirens are typically removed; and the lights are either disabled, or the red lens swapped for amber.
Fire trucks, esp. pumpers, are run hard - and have lots of idle hours.... The drivelines also tend to be more complicated than 'regular' trucks, there's typically a transfer case added to the driveline, to run the pump and/or hydraulics.