What is the past history? So the First two years either a Supervisor or Specialty unit had it. After that more likely went to regular unit. More likely pull a lot of tires tided with metal chains in order to soften the roads to cut for sings. Rainy days a lot of fun with them. Burn out. Just hit hard the brakes and punch the gas ( that is why the transfer case sound). The mount in the back is for the night vision cameras ( FLIR/ RECON). If didn’t have the governor, top speed were tried to be achieve. Count less engine running hours. And last – Hope the driver didn’t chew/dip tabaco on it.
You need to find a cheaper mechanic. Did he really say its $450 to replace a spare wheel??? And $800 for perfectly serviceable tyres to be replaced?? Goto a breakers yard for a wheel. Or get one off ebay, find somebody breaking a raptor for parts, and make an offer on one of the wheels… With those tyres, use them until you actually need to replace them. Thats an instant saving of $1200.
This might be news to you, but having been a cop and a police department fleet manager, I can tell you that, while driven hard daily, police vehicles are usually very well-maintained and when things break, they get fixed. That's the benefit of having Uncle Sam's deep pockets.