I’d be concerned about the lifetime costs of the vehicle regarding maintenance, repair, and replacement parts. I’d guess that insurance would be much higher too depending on how that’s handled. Would chip shortages cause issues?
So far, data shows that well-made EVs have lower maintenance and repair costs than legacy vehicles in similar categories. There are definitely some fairly unreliable EVs—early leafs with horrible batteries (early technology), and exploding chevy bolts (GM...you tell me), but that isn't true for the latest or high end vehicles. Also, the USPS is self-insured (and therefore insurance costs are irrelevant), and chip shortages would really only impact the steady delivery of vehicles and (to a lesser extent) service parts.